Rolling apparatus

ABSTRACT

The bearing rings  1  and  2  of a rolling bearing is formed of one kind of titanium alloys of β type titanium alloys, near β type titanium alloys and α+β type titanium alloys. The titanium alloy has a surface hardness of Hv 400 or more and less than Hv 600 for increasing the corrosion resistance and wear resistance of the bearing ring. Spherical rolling elements  3  rolling on the raceway surfaces  1   a  and  2   a  of the bearing rings  1  and  2  are formed of ceramics such as silicon nitride. When β type titanium alloys or α+β type titanium alloys after a solution treatment and applied with an oxidation treatment at a low temperature of 400 to 600° C. are used as the material for the bearing ring, a bearing ring made of titanium alloy suitable to use under a circumstance requiring corrosion resistance is obtained.

TECHNICAL FIELD

This invention concerns a rolling device such as a rolling bearing, aball screw and a linear guide and, more in particular, it relates to arolling device suitable to use, for example, in semiconductor productionapparatus, chemical fiber production machines, liquid crystal panelproduction apparatus, and equipments using electron beams or X-rays.

BACKGROUND ART

In rolling bearings such as ball bearings, bearing rings and rollingelements thereof are generally formed of iron and steel materials suchas high carbon chromium bearing steels and case hardening steels androlling bearings are used in various working circumstances. Accordingly,in machines that use water or sea water such as food machines orchemical fiber production machines, since rust is formed on the surfacesof bearing rings and rolling elements due to water or sea waterintruding into the inside of bearings making them no more usable,rolling bearings in which bearing rings or rolling elements are formedof austenitic stainless steels such as SUS 440C are mainly used.

While such rolling bearings have good corrosion resistance to water orsea water, corrosion resistance to chemicals, for example, acidicsolutions such as sulfuric acid or alkaline solutions can not be saidfavorable. In view of the above, rolling bearings in which bearing ringsare formed of titanium alloys have often been used in machines that usechemicals, for example, acidic solutions such as sulfuric acid oralkaline solutions, for example, semiconductor production apparatus andliquid crystal panel production apparatus. However, titanium alloys lackin the surface hardness when merely applied with usual solutiontreatment or aging treatment and can not be used as they are as thematerial for the bearing ring of the rolling bearing. Accordingly, whentitanium alloy is used as the material for the bearing ring of therolling bearing, it is necessary to increase the surface hardness of thetitanium alloy by some or other methods.

As a method of increasing the surface hardness of the titanium alloys, amethod of increasing the surface hardness of β-titanium alloy to thesurface hardness of Hv 600 or more is disclosed in Japanese PublishedUnexamined Patent Application No. Hei 11-22221. However, according tothe method disclosed in this publication, α-phase has to be precipitatedin excess in the β type titanium alloy and since the α-phase is poor inthe corrosion resistance compared with the β-phase, the corrosionresistance is sometimes insufficient depending on the workingcircumstance. Further, in the method disclosed in this publication, itis necessary to apply shot peening after cold working to result in aproblem of increasing the cost by the increase in the number of stepssuch as cold working or shot peening.

Further, in equipments used in semiconductor production steps, forexample, an electron beam lithography system or a wafer inspectionapparatus, laser beams have been used so far as a means for writingcircuit patterns on a wafer but along with the micro-miniaturization ofthe circuit patterns, electron beams having shorter wavelength andhigher resolution power than the laser beams have been used in recentyears. In the electron beam lithography system or the wafer inspectionequipment using the electron beams, the electron beams are deflectedeasily when disturbance is present in peripheral magnetic fields tosometimes lower the writing accuracy or inspection accuracy.Accordingly, in a case of using rolling bearings to such apparatus, itrequires such a rolling bearing that does not disturb the peripheralmagnetic fields by the rotation of the bearing ring and, in order tosatisfy such a demand, use of non-magnetic stainless steel or berylliumcopper as the material for the bearing ring of the rolling bearing hasbeen investigated.

However, since the permeability of the non-magnetic stainless steel isabout 1.04 to 1.002, when the non-magnetic stainless steel is used asthe material for the bearing ring of the rolling bearing, it has apossibility of causing disturbance in the peripheral magnetic fieldswhen the bearing ring is magnetized even slightly. On the other hand,beryllium copper has a permeability of 1.001 or less and has lesspossibility of causing disturbance in the peripheral magnetic fields asin the non-magnetic stainless steel. However, since a portion ofelements or compounds thereof constituting beryllium copper isconsidered as environmental load substances, its use may sometimessuffer from restriction. Further, since it is expected that theenvironmental problem will be considered more important in the future,use of beryllium copper itself may possibly be limited. Further, sinceberyllium copper has a highest hardness of about Hv 400, it involves aproblem of tending to cause early wear during use under large load.

OBJECT OF THE INVENTION

A first object of the present invention is to provide a rolling devicethat can be used favorably over an extended period of time even in ahighly corrosive circumstance.

A second object of the present invention is to provide a rolling devicesuitable to use in machines that use strongly acidic solutions such assulfuric acid or strongly alkaline solutions.

A third object of the present invention is to provide a rolling devicethat can be used favorably over an extended period of time also in acircumstance where non-magnetic property is required.

A fourth object of the present invention is to provide a rolling devicesuitable to use in equipments using electron beams or X-rays such as awafer inspection apparatus or nuclear magnetic resonance diagnosticapparatus.

A fifth object of the present invention is to provide a rolling devicethat can be used favorably over an extended period of time also in acircumstance where a lubricant such as grease can not be used.

SUMMARY OF THE INVENTION

A rolling device according to this invention comprises an outer memberand an inner member each having a raceway surface and rolling elementsrolling on the raceway surface by rotational or linear movement of theouter member or the inner member in which the outer member and/or theinner member is constituted with at least one kind of titanium alloys ofβ type titanium alloys, near β type titanium alloys and α+β typetitanium alloys.

In a preferred embodiment of the present invention, the titanium alloyhas a surface hardness of Hv 400 or more and less than Hv 600. Further,the titanium alloy has a core hardness of Hv 420 or more, preferably, Hv450 or more and has an oxygen compound layer on the surface in which theoxygen compound layer comprises a titanium oxide containing rutile typeTiO₂ and has a thickness of 20 nm or more and, preferably, 50 nm ormore.

In a preferred embodiment of the present invention, the rolling elementis constituted with at least one kind of materials of titanium alloys,silicon nitride, silicon carbide, zirconia series ceramics, aluminaseries ceramics and SIALON series ceramics.

In another preferred embodiment of the present invention, the rollingdevice further comprises a cage for holding the rolling elements and thecage has a heat conductivity of 20 W/(m·K) or more. Further, the cage isconstituted, preferably, with one kind of materials of copper, telluriumcopper, brass, aluminum bronze, phosphorus bronze, nickel silver, cupronickel and beryllium copper.

In a further preferred embodiment of the present invention, at least oneof the outer member, the inner member and the rolling elements isconstituted with a titanium alloy and the titanium alloy has a ω phasewith the size of the crystal particles of 1 μm or less, preferably, 800nm or less and, further preferably, 10 nm or less.

In a further preferred embodiment of the present invention, the outermember and/or the inner member has a hard film on the raceway surface.The hard film is constituted with at least one kind of materials of TiN,TiC, TiCN, TiAlN, CrN, SiC and diamond-like carbon, and the racewaysurface formed with the hard film has a surface hardness of Hv 350 ormore and, preferably, Hv 450 or more. Further, the outer member and/orthe inner member has a lubricating film of 0.1 μm to 10 μm and,preferably, 0.1 μm to 5 μm on the hard film.

In a further preferred embodiment of the present invention, the rollingelement is constituted with a superhard alloy and or cermet and has aheat conductivity of 35 W/(m·K) or more, preferably, 50 W/(m·K) or more.

In a further preferred embodiment of the present invention, the rollingelement is constituted with an iron and steel material and has thesurface hardening layer having corrosion resistance on the surface andthe surface hardening layer is formed by applying a chromium diffusionpenetration treatment or a nitridation treatment to the surface of abase material constituting the rolling element.

In a further preferred embodiment of the present invention, the titaniumalloy is a titanium alloy satisfying the condition: 3.7≦(H/E),preferably, 4.0≦(H/E) and, further preferably, (H/E)≦4.5 where E (Gpa)represents the Young's modulus and H (Hv) represents the minimumhardness for the portion from the raceway surface to a depthcorresponding to {fraction (2/100)} to {fraction (5/100)} for thediameter of the rolling element.

In a further preferred embodiment of the present invention, the ratioα₂/α₁ between the heat expansion coefficient α₁ of the titanium alloyand the heat expansion coefficient α₂ of the rolling element is within arange of 0.4 to 1.3.

In a further preferred embodiment of the present invention, a sealedplate for shielding an opening formed between the outer member and theinner member is formed of titanium at a purity of 99.5% or higher andthe outer member and the inner member each has an oxide film comprisingTiOx (in which 0<x<2) on the surface.

The β-type titanium alloy and the α+β type titanium alloy increase thehardness by fine precipitation of the α-phase in the β-phase by applyinga solution treatment to the titanium alloy from the vicinity of thetemperature at which the α-phase transforms into the β-phase totransform the metal structure substantially into the β-phase and thenapplying an aging treatment to the titanium alloy. However, when theα-phase is precipitated by the aging treatment, β-stable alloyingelements are concentrated in the β-phase along with preparation of theα-phase. Accordingly, local corrosion tends to occur due to thedifference of the corrosion resistance between the α-phase and theβ-phase along with increase in the precipitation amount of the α-phase.Accordingly, it is necessary that the β-phase in the β-type titaniumalloy or the α+β type titanium alloy remains to some extent in orderthat the alloy can be used suitably also in a highly corrosivecircumstance but, since the β-phase is soft compared with the α-phase,the wear resistance is insufficient when the amount of the β-phase isexcessive while the corrosion resistance is improved.

The present inventors have made an earnest study on the solutiontreatment and the aging treatment of the titanium alloy and have foundthat a titanium alloy which is satisfactory as the material for thebearing ring of a rolling element can be obtained by applying a lowtemperature oxidation treatment to the titanium alloy after the solutiontreatment such that the surface hardness of the titanium alloy is Hv 400or more and less than Hv 600. Then, since the hardness of Hv 400 or moreand less than 600 is a hardness comparable with that of the stainlesssteels such as SUS 630 or YHD50 (trade mark) used so far as the bearingmaterial for the special circumstances, it can be used sufficiently asthe material for the bearing element in a circumstance where a largeload is not applied by so much.

The surface of a portion of the bearing ring that is in contact with therolling element has an elliptic shape that is referred to as a contactellipse and the area is extremely small. Accordingly, when stress isapplied to the bearing ring, an extremely large surface pressure exertson the contact ellipse. When the bearing ring of the rolling bearing isformed of a titanium alloy (Young's modulus: about 100 Gpa) and therolling element is formed of a stainless steel (Young's modulus: about200 Gpa), this means that the bearing ring deforms more greatly than therolling element and the area of the contact ellipse in contact with therolling element increase. In view of calculation, the area of thecontact ellipse of a bearing ring made of titanium alloy is larger thanthat of the bearing ring made of a stainless steel and the maximumcontact surface pressure at the contact ellipse of the bearing ring madeof titanium alloy is about 0.8 times that of the bearing ring made ofstainless steel. Accordingly, since the contact area with the rollingelement is larger in the bearing ring made of the titanium alloy than inthe bearing ring made of the stainless steel, the contact pressuresurface is lowered and the rolling fatigue is moderated preferably.

However, when the surface hardness of the bearing ring made of thetitanium alloy is less than Hv 400, wear tends to be caused abruptlyeven when the surface pressure is low. Further, indentations are tend tobe caused upon intrusion of obstacles such as dusts to shorten the lifeof the rolling bearing. Accordingly, it is necessary for the bearingring made of the titanium alloy that the surface hardness is Hv 400 ormore and the surface hardness of the bearing ring made of the titaniumalloy is more preferably Hv 450 or more when higher wear resistance isrequired. Further, when corrosion resistance or wear resistance isfurther required, the titanium alloy can be provided with higherhardness and corrosion resistance by surface hardening heat treatmentsuch as a nitridation treatment or an oxidation treatment.

The permeability of a titanium alloy is 1.001 or less and the value isnearly equal with that for the substantially complete non-magneticproperty. Accordingly, since peripheral magnetic fields suffer from noeffects by the rotation of the bearing ring, it can be used favorably toequipments using electron beams or X-rays. However, if the rollingelement or the cage is not a non-magnetic body, magnetization thereofcauses deterioration of the accuracy in the apparatus described above bymagnetization thereof. Accordingly, when a substantially completenon-magnetic property is required for the rolling device, it isnecessary that the permeability of the rolling element and the cageshould also be 1.001 or less like that in the permeability of thebearing ring made of the titanium alloy.

The material for the rolling element with the magnetic permeability of1.001 or less can include titanium alloys, as well as ceramics such assilicon nitride, silicon carbide, zirconia series ceramics, aluminaseries ceramics and SIALON series ceramics or titanium alloys. Further,the material for the cage with the permeability of 1.001 or less caninclude resins such as polyamide and fluoro resins or non-magneticmetals such as brass and SUS 304.

When the materials are investigated in details, in the cage made ofstainless steels typically represented by SUS 304, martensite is formedby strain induced transformation upon pressing. Accordingly, the cage istended to be magnetized to result in a possibility of increasing themagnetic field fluctuation due to the rotation of the cage. Further, inrecent years, specific permeability lower than 1.01 to 1.1 of thenon-magnetic stainless steel, specifically, about 1.001 is demanded andthe use of the cage made of the non-magnetic stainless steel issometimes restricted. Accordingly, it is desirable that the rollingelement is made of ceramics, while the cage is made of a copper seriesalloy.

The titanium alloy is a substantially complete non-magnetic body andceramics are also complete non-magnetic body. On the other hand, thecopper alloy is a non-magnetic material with the permeability lower thanthat of the non-magnetic stainless steel and the specific permeabilitythereof is 1.001 or less. Accordingly, even when it is used under amagnetic circumstance, since rotation of the cage does not causefluctuation of magnetic fields, it is suitable as a cage made of metalin a rolling device used under a non-magnetic circumstance.

Further, since the copper alloy has self-lubricity, frictioncharacteristics at the contact surface with the rolling element and atthe guiding surface of the bearing ring are improved and the amount ofwear is small even under a circumstance where a lubricating oil orgrease can not be used or a non-magnetic and vacuum circumstance as inelectron beam equipments or semiconductor production apparatus.

Further, since the cage made of the copper alloy has a high heatconductivity and causes no heat accumulation on the sliding guidesurface, adhesive wear can be suppressed. Further, the copper alloy hashigh heat dissipation, can promote heat dissipation along with rotationof the cage and can suppress the temperature elevation of the bearing.On the contrary, in a case where the bearing is made of the titaniumalloy and the cage is made of austenitic non-magnetic stainless steelsuch as SUS 304, since the heat conductivity and the specific heat ofSUS 304 are small, temperature locally rises remarkably at a slidingportion between the cage and the bearing ring guide surface tending tocause adhesive wear relative to the bearing ring. Since the heatconductivity of the austenitic non-magnetic stainless steel such as SUS304 is 16 W/(m·K), it is preferred, for the cage made of the copperalloy to use a cage made of a copper alloy having a heat conductivity of20 W/(m·K) or more and, more preferably, 35 W/(m·K) or more.

Referring to the kind of the copper alloy, any of copper alloys can beused suitably so long as it has the heat conductivity of 20 W/(m·K) ormore, for example, copper alloy castings such as pure copper, telluriumcopper, brass, freely cutting brass, high strength brass, and aluminumbronze or stretchable copper alloys such as pure copper, tellurium,phosphorus bronze, nickel silver and cupro nickel or precipitationhardening type beryllium copper. However, since low alloys such as purecopper and tellurium copper have low strength and hardness, it isdesirable to use copper alloys excluding them in a case where particularimportance is attached to the wear resistance.

It is considered that the surface treatment such as an oxidationtreatment or a nitridation treatment should be applied at a hightemperature of 600° C. or higher for insuring the thickness of thecompound layer and diffusion promotion of intruded elements. However,when the titanium alloy is heated in oxygen or oxygen-containing gas fora predetermined period of time, since titanium has a high affinity withoxygen, an oxygen compound such as TiO₂ or Ti₃O is formed on the surfaceeven at a relatively low temperature of 400 to 600° C.

The oxygen compound such as TiO₂ formed on the surface of the titaniumalloy by the oxidation treatment is a highly chemically stablesubstance. On the other hand, the surface of the titanium compound tendsto become highly reactive by sliding movement with the rolling elementor the like, by which adhesive wear tends to be caused so that it isconsidered to be poor in the wear resistance. However, since the surfaceis covered with the highly chemically stable compound by applying theoxidation treatment to the titanium alloy, surface activation issuppressed and, as a result, seizure less occurs to improve the slidingproperty and the wear resistance.

Further, when the thickness of the oxygen compound layer formed on thesurface of the titanium alloy by the oxidation treatment is 20 nm ormore, the load carrying capacity increases to remarkably improve theeffect of the wear resistance and sliding property. However, when thethickness of the oxygen compound layer is less than 20 nm, the effect ofimproving the wear resistance and the sliding property is small.Accordingly it is desirable that the thickness of the oxygen compoundlayer is 20 nm or more. Further, for obtaining better wear resistanceand sliding property, it is preferred that the thickness of the oxygencompound layer is 50 nm or more.

When the titanium alloy is put to the oxidation treatment at a hightemperature of 700° C. or higher, the oxygen compound layer formed onthe surface of the titanium alloy mainly comprises rutile type TiO₂ andthe thickness of the oxygen compound layer also increases. Accordingly,durability to great load is improved, but the surface roughness of thetitanium alloy is sometimes deteriorated on the other hand to increasethe rotational torque of the bearing.

On the other hand, when the titanium alloy is put to the oxidationtreatment at a temperature of 400 to 600° C., the oxygen compound layerformed on the surface of the titanium alloy is in a state where TiO_(x)oxide such as rutile type TiO₂ and Ti₃O (x:0<x<2) and Ti are presenttogether, which is more dense compared with the oxygen compound layermainly comprising rutile type TiO₂. Accordingly, the surface roughnessafter the oxidation treatment is favorable and, as a result, therotational torque of the bearing is lowered and detachment of thecompound layer or the like is less caused.

FIG. 10A shows a heat treatment step for the solution treatment and theaging treatment conducted generally as a method of hardening the β typetitanium alloy and the α+β type titanium alloy. In this heat treatmentmethod, since the titanium alloy tends to be oxidized abruptly, heatingis often conducted in a high vacuum atmosphere or in an inert gasatmosphere such as argon.

FIG. 10B shows a gas oxidation treatment at high temperature. In thiscase, it is often used after the oxidation treatment as it is but, sinceheating is conducted at a high temperature for a long time without thesolution treatment and the aging treatment, the core hardness is loweredto sometimes give undesired effects on the rolling life. Further, asdescribed above, it may be a worry of causing degradation in the surfaceroughness and brittlement of the compound layer.

FIG. 10C shows a method of an oxidation treatment at a low temperatureof 400 to 600° C. for the titanium compound after the solutiontreatment. Since the temperature for the oxidation treatment of 400 to600° C. is within a range of the temperature identical to that uponaging treatment after the solution treatment of the β type titaniumalloy and the α+β type titanium alloy, it can serve both as theoxidation treatment and the aging treatment. Accordingly, it does notincrease the cost due to the increase in the number of steps.

Further, since the hardness is improved to Hv 420 or more by the agingtreatment not only for the surface of the titanium alloy but also forthe core of the titanium alloy, the rolling life is improved. Further,since the processing temperature is low, thermal deformation is small togive less possibility of deteriorating the dimensional accuracy of thebearing ring. However, when the core hardness is less than Hv 420, sincethe effect for extending the rolling life of the bearing is small evenwhen it has the oxygen compound layer on the surface, it is desirablethat the hardness of the core obtained by the oxidation treatment alsoserving as the aging treatment is Hv 420 or more. Further, for obtaininga more stable extending effect of the rolling life, it is preferred toincrease the core hardness of the titanium alloy to Hv 450 or more.

The oxidation treatment is conducted in a gas atmosphere such as inoxygen or an oxygen-containing gas. For example, it is conducted inatmospheric air, in a 90% N₂+10% O₂ gas or in a gas in which apredetermined amount of H₂O gas is mixed to an Ar gas. However, the kindof the gas in the oxidation treatment atmosphere is not restricted solong as the oxygen compound layer containing rutile type TiO₂ and havinga thickness of 20 nm or more can be formed on the surface by applyingthe oxidation treatment. Further, in order to prevent abrupt oxidation,the oxidation can also be conducted using the gas described above in astate of reducing the pressure in the heating furnace.

As the titanium alloy for which the oxidation treatment is applied, α+βtitanium alloy or β type titanium alloy that increases the hardness bythe solution treatment and the aging treatment can be used suitably.They include, for example, Ti-6Al-4V, Ti-15V-3Cr-3Sn-3Al, Ti-22V-4Al andTi-15Mo-5Zr-3Al. There is no restriction on the kind so long as thetitanium alloy forms an oxygen compound layer containing rutile typeTiO₂ and having a thickness of 20 nm or more on the surface with thecore hardness being Hv 420 or more by applying the oxidation treatment.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a vertical cross sectional view of a rolling bearing accordingto an embodiment of the present invention.

FIG. 2 is a view showing a test apparatus used upon testing of a rollinglife of a rolling bearing.

FIG. 3 is a view showing a relation between the result of a corrosionresistant test of rolling bearing and the surface hardness of bearingrings made of titanium alloy.

FIG. 4 is a view showing a relation between the result of a rolling lifetest of rolling bearing and the surface hardness of bearing rings madeof titanium alloy.

FIG. 5 is a view showing a method of measuring the change in magneticflux density in peripheral magnetic fields.

FIG. 6 is a view showing a signal waveform outputted from a tesla metershown in FIG. 5.

FIG. 7 is a view showing a method of testing the wear resistance of abearing ring made of titanium alloy.

FIG. 8 is a view showing a relation between the result of a wearresistance test of bearing rings made of titanium alloy and thethickness of an oxygen compound.

FIG. 9 is a view showing a relation between the result of a rolling lifetest of bearing ring made of titanium alloy and a hardness for the core.

FIG. 10A is a view showing an existent method upon hardening a titaniumalloy.

FIG. 10B is a view showing a method upon hardening a titanium alloy by ahigh temperature oxidizing treatment.

FIG. 10C is a view showing a method upon hardening a titanium alloy by alow temperature oxidizing treatment.

FIG. 11A is a side elevational view of a Sawin type wearing testingmachine.

FIG. 11B is a front elevational view of a Sawin type wearing testingmachine.

FIG. 12 is a fragmentary cross sectional view of a rolling bearingaccording to another embodiment of the present invention.

FIG. 13 is a view for explaining a gas nitridation treatment applied toa bearing ring made of a titanium alloy.

FIG. 14 is a schematic view of an apparatus for forming a hard film onthe surface of a bearing ring made of a titanium alloy.

FIG. 15 is a cross sectional view of a test apparatus used upon testingdurability of a thrust rolling bearing.

FIG. 16 is a view showing a relation between the surface hardness ofbearing ring made of a titanium alloy and a peeling life of a hard filmformed on the surface of the bearing ring.

FIG. 17 is a schematic view of an apparatus for testing durability of aradial rolling bearing in vacuum.

FIG. 18 is a view showing a relation between heat conductivity and awearing ratio of a rolling element,

FIG. 19 is cross sectional view of a rolling bearing in anotherembodiment of this invention.

FIG. 20 is a view showing a relation between indentation resistance testand H/E of a rolling bearing.

FIG. 21 is a view showing a relation between rolling life test and H/Eof a rolling bearing.

FIG. 22 is a view showing a fluctuation pattern of circumstantialtemperature.

FIG. 23 is a view showing the relation between the ratio of the linearexpansion coefficient of a bearing ring and a linear expansioncoefficient of a rolling element and a rolling life of a rollingbearing.

FIG. 24 is a cross sectional view of a rolling bearing as an otherembodiment according to this invention, and

FIG. 25 is a schematic view of a testing apparatus for testing wearresistance of a rolling bearing.

DESCRIPTION OF THE INVENTION

The rolling device according to the present invention is to be explainedmore specifically with reference to the appended drawings.

FIG. 1 is a cross sectional view of a rolling bearing according to anembodiment of the present invention. A rolling bearing shown in FIG. 1is a ball bearing of bearing No. 6001 (12 mm inner diameter, 28 mm outerdiameter and 8 mm width) comprising an outer ring 1, an inner ring 2,rolling elements 3, a cage 4 and seals 5.

The bearing rings 1 and 2 are formed of one kind of titanium compoundsof Ti-6Al-4V, Ti-15Mo-5Zr-3Al and Ti-15Mo-5Zr. A spherical rollingelement 3 conducts rolling movement on rolling surfaces 1 a and 2 aduring rotation of one of the bearing rings 1 and 2. The rolling element3 is formed of silicon nitride and the cage 4 holding the rollingelement 3 is formed of a fluoro resin.

The bearing rings 1 and 2 made of titanium alloy are machined into apredetermined shape and then applied with a solution treatment and anaging treatment. The rolling surfaces 1 a and 2 a of the bearing rings 1and 2 are applied with grinding after applying the solution treatmentand the aging treatment. The solution treatment was applied by keepingthe titanium alloy at a temperature of 950° C. to 1000° C. in a casewhere the titanium alloy is Ti-6Al-4V and at a temperature of 800° C. to850° C. in a case where the titanium alloy is Ti-15Mo-5Zr-3Al orTi-15Mo-5Zr for one hour and then the titanium alloy was cooled withwater for solution treatment.

The aging treatment for the titanium alloy was conducted under thetreating conditions at 350° C. to 500° C. for 3 hours to 40 hours.Cooling was conducted usually by air cooling and the cooling rate wasretarded by furnace cooling for those titanium alloys which are requiredto improve the hardness by making the precipitated tissue finer.Further, for those titanium alloys which are required to precipitate theα-phase more uniformly and finely, a two step aging treatment ofapplying an aging treatment under the conditions at 425° C. for 17 hoursat first and then applying an aging treatment under the conditions at475° C. for 7 hours was adapted.

Corrosion Resistance Test

Test specimens were manufactured with materials for bearing rings shownin Table 1 and the following corrosion resistance test was conducted foreach of the manufactured test pieces. That is, each of the testspecimens in Table 1 was immersed in a 5N—H₂SO₄ sulfuric acid solutionat about 25° C., the weight of the test specimens before immersing inthe sulfuric acid solution and after immersing for about 24 hours in thesulfuric acid solution were measured and the decrease in the weight withthe sulfuric acid solution was evaluated.

TABLE 1 Surface corrosion loss in Rolling life Material for hardnessH₂SO₄ ratio in salt No. bearing ring Aging condition (Hv) (g) waterExample 1 Ti-6Al-4V 500° C. × 6 h 406 0.0002 2.2 2 Ti-6Al-4V 450° C. ×20 h (Furnace 427 0.0002 2.5 cooling) 3 Ti-15Mo-5Zr-3Al 450° C. × 16 h453 0.0001 2.4 4 Ti-15Mo-5Zr-3Al 425° C. × 17 h + 475° C. × 7 h 4790.0001 2.9 (Furnace cooling) 5 Ti-15Mo-5Zr 450° C. × 20 h (Furnace 5520.0002 3.0 cooling) 6 Ti-15Mo-5Zr 350° C. × 40 h 592 0.0001 3.5 Comp. 1′Ti-6Al-4V 500° C. × 3 h 361 0.0002 1.0 Example 2′ Ti-15Mo-5Zr-3Al 450°C. × 8 h 393 0.0001 1.3 3′ Ti-15Mo-5Zr-3Al Cold cooling + 450° C. × 20 h605 0.0005 3.2 4′ Ti-15Mo-5Zr Cold cooling + 450° C. × 20 h 615 0.00083.7 5′ Ti-15Mo-5Zr Cold cooling + 350° C. × 40 h 630 0.001 3.5 6′SUS440C — 670 0.5 0.9 7′ SUS630 — 455 0.1 1.2 8′ Beryllium copper — 3970.009 1.0

Rolling Life Test

Then, rolling bearings for use in the test were manufactured with thematerials shown in Table 1 and the following rolling life test wasconducted in an aqueous NaCl solution at 5% by weight concentration foreach of the manufactured test bearings. That is, as shown in FIG. 2,after setting a test bearing 10 to a rotational shaft 13 of a tester, anaxial load of about 19.6 N and an axial load of about 49 N were loadedby a spring 14 and a wire 15 and, in this state, the rotational shaft 13was rotated at a speed of about 1000 rpm by a motor 12. Then, afterrotating the inner ring of the test bearing by a predetermined number ofcycles, the wearing amount on the rolling surface was measured.

Table 1 shows the test result in the corrosion resistance test (decreasein the weight) and FIG. 3 shows a relation between the test result ofthe corrosion resistance test and the surface hardness of titaniumalloys.

As can be seen from Table 1 and FIG. 3, Nos. 1-6 corresponding to theexamples of the present invention show smaller values for the reductionof weight in the sulfuric acid solution compared with Nos. 6′ to 8′ asthe comparative examples. This is because the bearing rings of Nos. 6′to 8′ are formed of stainless steel or beryllium copper, whereas bearingrings of Nos. 1 to 6 are formed of a titanium alloys.

Further, Nos. 1 to 6 corresponding to the examples of the presentinvention show smaller values for the reduction of weight in thesulfuric acid solution compared with Nos. 3′ to 5′ as the comparativeexamples. This is because the surface hardness of the bearing rings madeof titanium alloys is Hv 600 or more in Nos. 31 to 5′, whereas thesurface hardness of the bearings rings made of the titanium alloy isless than Hv 600 in Nos. 1 to 6.

Then, Table 1 shows the test result of the rolling life test (rollinglife ratio) and FIG. 4 shows a relation between the test result of therolling life test and the surface hardness of the rolling bearing madeof the titanium alloy. The rolling life ratios in Table 1 and FIG. 4 arecomparative values in a case of evaluation based on the rolling life ofNo. 1′ being assumed as 1.

As can be seen from Table 1 and FIG. 4, Nos. 1 to 6 corresponding to theexamples of the present invention show larger values for rolling liferatio in salt water compared with Nos. 1′ and 2′ as the comparativeexamples. This is because the surface hardness of the bearing rings madeof the titanium alloy is less than Hv 400 in Nos. 1′ to 2′, whereas thesurface hardness of the bearing rings of the titanium alloy is Hv 400 ormore in Nos. 1 to 6.

From the foregoings, it can be seen that rolling bearings that can beused suitably for a long period of time even under such a circumstancewhere corrosion resistance is required against corrosive fluids such assaline or sulfuric acid can be obtained by making the bearing ring ofthe rolling bearing of the titanium alloy and setting the surfacehardness for the bearing ring material to less than Hv 600 and Hv 400 ormore.

Measuring Test for the Change of Magnetic Flux Density

Rolling bearings for use in test were manufactured with materials shownin Table 2A and Table 2B, and the following test for measuring thechange of magnetic flux density was conducted to each of themanufactured test bearings. That is, as shown in FIG. 5, after attachinga test bearing 10 to a rotational shaft 13 rotated in an magnetic fieldof a permanent magnet 16, the rotational shaft 13 was rotated at a speedof about 500 rpm and the change of the magnetic flux density wasmeasured by a tesla meter 17. Then, those showing the maximum output ofthe tesla meter 17 (refer to FIG. 6) of 0.1 mT or more were evaluated aswith change of the magnetic flux density, whereas those showing themaximum output of less than 0.1 mT were evaluated as with no change ofthe magnetic flux density.

Table 2A shows the test result for the test of measuring the change ofmagnetic flux density while Table 2B shows the magnetic permeability ofmaterials shown in Table 2A.

TABLE 2A Test Magnetic flux No. Bearing ring Rolling element Cage changeExample 11 Ti-6Al-4V Si₃N₄ Resin No 12 Ti-6Al-4V Alumina ceramics ResinNo 13 Ti-15Mo-5Zr-3Al Si₃N₄ Resin No 14 Ti-15Mo-5Zr-3Al SiC Resin No 15Ti-15Mo-5Zr Si₃N₄ Resin No 16 Ti-15Mo-5Zr Zirconia Resin No ceramicsCom. 11′ Ti-6Al-4V Si₃N₄ SUS304 Changed Example 12′ Ti-15Mo-5Zr-3AlSUS440C Resin Changed 13′ Ti-15Mo-5Zr SUS440C Resin Changed 14′ Becopper Si₃N₄ SUS304 Changed 15′ Non-magnetic stainless Si₃N₄ ResinChanged steel

TABLE 2B Material Permeability Bearing Ti-6A1-4V 1.001 or less ringTi-15Mo-5Zr-3A1 1.001 or less Ti-15Mo-5Zr 1.001 or less Be copper 1.001or less Non-magnetic stainless More than steel 1.001 Rolling Si₃N₄ 1.001or less element SiC 1.001 or less Zirconia ceramics 1.001 or lessAlumina ceramics 1.001 or less SUS440C More than 1.001 Cage Resin 1.001or less SUS304 More than 1.001

As can be seen from the test result of Table 2A, Nos. 1 to 6corresponding to the examples of the present invention show less changeof magnetic flux density compared with Nos. 11′ and 14′ as thecomparative example. This is because the cage is formed of SUS 304 inNos. 11′ and 14′, whereas the cage of is formed of a resin in Nos. 1 to6.

Further, Nos. 1 to 6 corresponding to the examples of the presentinvention show less change of magnetic flux density compared with Nos.12′ and 13′ as the comparative examples. This is because the rollingelements are formed of SUS 440C in Nos. 12′ and 13′, whereas the rollingelements are formed of ceramics such as silicon nitride in Nos. 1 to 6.

Further, Nos. 1 to 6 corresponding to the examples of the presentinvention show less change of magnetic flux density compared with No.15′ as the comparative example. This is because the bearing ring isformed of the non-magnetic stainless steel in No. 15′, whereas thebearing rings are formed of the titanium alloy in Nos. 1 to 6.

Accordingly, it can be seen that since the magnetic flux density ofperipheral magnetic fields does not change greatly by the rotation ofthe bearing by making the bearing ring with the titanium alloy, therolling elements with the ceramics and the cage with the resin, rollingbearings favorable for the use under the circumstance where non-magneticproperty is required can be obtained.

Wear Test for Cage

Cages were manufactured with materials shown in Table 3, which wereincorporated into test bearings where the bearing ring comprisedTi-15Mo-5Zr-3Al and the rolling element comprised Si₃N₄ and a wearingtest for the cage was conducted. Specifically, each of the test bearingswas rotated under the conditions at a rotational speed: 200 rpm, under aradial load: 49.0 N, axial load: 19.6 N, at a vacuum degree: 1×10-5 Torrand in lubrication state: non-lubrication. Then, the weight of the cagebefore rotation of the test bearing and the weight of the cage at theinstance the rotation of the test bearing reached 1×10⁷ were measured,and the difference was evaluated as the amount of wear of the cage.

TABLE 3 Name of No. material Cu Zn Pb Sn Al Fe Mn Ni P Others 21 YBsC185.3 14.2 0.3 — — — — — — 22 YBsC2 67.8 28.8 2.5 0.5 0.2 — — — — 23HBsC1 58.8 36.5 0.2 0.2 0.7 0.7 2.3 0.2 — 24 HBsC2 58.5 37.3 0.2 0.2 1.30.5 1.6 — — 25 AlBC1 77.2 — — — 8.3 3.3 0.9 2.2 — 26 AlBC3 79.7 — — —9.6 4.4 1 4.8 — 27 LBC3 78.7 0.8 9.7 10 — — — 0.4 — 28 LBC4 74.6 0.514.8 9.6 — — — 0.2 — 29 C5191 93 — — 6.5 — — — — 0.27 0.27 30 C5210 91.5— — 8.1 — — — — 0.27 Be: 1.89 31 C17210 97.6 — — — — — — — — 32Cupronickel 69.8 — — — — — — 29.8 — 33 Echobrass 75.4 21.2 — — — — — — —Si: 3.0 34 C1100 99.9 — — — — — — — — 35 C14500 99.3 — — — — — — — 0.008Te: 0.51

The bearing rings made of titanium alloys for the test bearings usedwere formed of titanium alloys applied with a solution treatment underthe conditions at 800 to 850° C.×1 hr, cooled by water and then appliedwith a first age hardening treatment under the conditions at 425° C.×20hrs and further applied with a second age hardening treatment under theconditions at 475° C.×7 hrs for obtaining a surface hardness of Hv 480or more.

No. 33 “Echobrass” in Table 3 is a name of commercial productsmanufactured by Sanpo Shindo Kogyo Co., Ltd.

Table 4 shows the test result for the cage wear test (wear ratio). Thewear ratios for respective cages in Table 4 are comparative values in acase of evaluation based on the wear amount of No. 21′ being assumed as1.

TABLE 4 Heat Material for Specific change of magnetic conductivity Wearcage permeability field W/(m · K) ratio Example 21 YBsC1 1.001 or lessNo 159 0.75 22 YBsC2 ↑ ↑ 115 0.69 23 HBsC1 ↑ ↑ 87 0.56 24 HBsC2 ↑ ↑ 1230.54 25 AlBC1 ↑ ↑ 50 0.45 26 AlBC3 ↑ ↑ 36 0.48 27 LBC3 ↑ ↑ 47 0.75 28LBC4 ↑ ↑ 52 0.81 29 C5191 ↑ ↑ 80 0.55 30 C5210 ↑ ↑ 63 0.52 31 C17200 ↑ ↑84 0.1 32 Cupronickel ↑ ↑ 29 0.75 33 Echobrass ↑ ↑ 38 0.24 34 C1100 ↑ ↑390 0.88 35 C14500 ↑ ↑ 380 0.87 Comp. 21′ SUS304 1.001 or more Changed15 1 Example 22′ SPCC 1 ↑ 59 1.3

As can be seen from the result of Table 4, Nos. 21-35 corresponding tothe examples of the present invention show smaller values for the wearratio compared with No. 21′ as the comparative examples. This is becausethe heat conductivity of the material for the cage (stainless steel) isless than 20 W/(m·K) in No. 21′, whereas the heat conductivity of thematerial for the cage (copper alloy) is 20 W/(m·K) or more in Nos. 21 to35.

Further, Nos. 21 to 35 corresponding to the examples of the presentinvention show less change of magnetic flux density compared with No.22′ as the comparative example. This is because the specificpermeability of the material for the cage shows a value exceeding 1.001in No. 22′, whereas the specific permeability of the material for thecage shows the value of 1.001 or less in Nos. 21 to 35.

Accordingly, rolling bearings that can be used favorably even under acircumstance where a lubricant such as grease can not be use andnon-magnetic property is required can be obtained by increasing the heatconductivity of the material of the cage to 20 W/(m·K) or more andlowering the specific permeability of the material for the cage as 1.001or less.

Wear Evaluation Test

Disk-shaped test specimen each of 50 mm diameter were manufactured withmaterials shown in Table 5 and wear evaluation test was conducted toeach of the test specimens. Specifically, as shown in FIG. 7, a load wasapplied by way of rolling elements 31 made of silicon nitride to thesurface of a disk-shaped test specimen 33 and a cage 32 made of brasswas rotated at a speed of 1000 rpm while gradually increasing the loadapplied to the test specimen 33 in a range from 20 N to 90 N. Then, theload at the instance the rotational resistance of the cage 32 reached0.69 N-m was evaluated as a seizure load and the maximum wearindentation depth on the surface of the test specimen was measuredsimultaneously. In a case where the rotational resistance of the cage 32did not reach 0.69 N-m even when the load exceeded 98 N, the seizureload at the instance the load reached at 98 N was evaluated as therotational resistance of the cage 32.

Table 5 shows the seizure load and the maximum wear indentation depthfor each of the test specimens obtained by the wear evaluation test.

TABLE 5 Maximum Compound Rotational wear Kind of layer Core Seizureresistance indent Material for Oxidation compound thickness hardnessload at 98 N depth No. test piece condition (0 < x < 2) (nm) (Hv) (N)(N.m) (μm) Example 36 Ti-6Al-4V 500° C. × 40 h TiO₂, TiOx 75 455 98<0.23 1 37 Ti-6Al-4 550° C. × 20 h TiO₂, TiOx 80 429 98< 0.22 1 38Ti-6Al-4V 600° C. × 10 h TiO₂, TiOx 95 421 98< 0.24 1 39Ti-15V-3Cr-3Sn-3Al 475° C. × 50 h TiO₂, TiOx 65 430 98< 0.2 1 40Ti-22V-4Al 475° C. × 50 h TiO₂, TiOx 70 441 98< 0.21 1 41Ti-15Mo-5Zr-3Al 400° C. × 60 h TiO₂, TiOx 25 467 98< 0.18 2 42Ti-15Mo-5Zr-3Al 450° C. × 60 h TiO₂, TiOx 55 503 98< 0.17 1 43Ti-15Mo-5Zr-3Al 500° C. × 60 h TiO₂, TiOx 90 452 98< 0.21 1 Comp. 36′Ti-6Al-4V Only — 0 429 35  — 7 Example aging 37′ Ti-6Al-4V 600° C. × 20h TiO₂, TiOx 110 411 61  — 5 38′ Ti-6Al-4V 700° C. × 20 h TiO₂ 1800 37398< 0.46 2 39′ Ti-22Al-4V Only — 0 480 43  — 6 aging 40′ Ti-15Mo-5Zr-3Al400° C. × 20 h TiO₂, TiOx 15 448 46  — 4 41′ Ti-15Mo-5Zr-3Al 300° C. ×40 h TiO₂, TiOx 10 384 38  — 6 42′ SUS630 — — 0 465 98< 0.42 4 43′ YHD50— — 0 432 98< 0.45 5 44′ Be—Cu — — 0 418 98< 0.36 8

As can be seen from the test result in Table 5, the test specimens madeof the titanium alloys of Nos. 36-43 show larger seizure load comparedwith the test specimens made of the titanium alloys of No. 36′ and No.39′. This is because an oxide compound layer is not formed on thesurface of the test specimens made of the titanium alloys of Nos. 36′and 39′, whereas the oxide compound layer is formed on the surface ofthe test specimens made of titanium alloys of Nos. 36-43.

Further, the test specimens made of the titanium alloys of Nos. 36-43show less rotational resistance of the cage at the instance the loadreaches 98 N compared with the test specimen made of the titanium alloyof No. 38′ where the load reaches 98 N. This is because the testspecimen made of the titanium alloy of No. 38′ does not contain TiO_(x)(0<x<2) in the oxygen compound layer, whereas the test specimens made ofthe titanium alloys in Nos. 36-43 contain TiO₂ and TiO_(x) in the oxidecompound layer.

Further, the test specimen made of the titanium alloys of Nos. 36-43show larger seizure load compared with the test specimens made of thetitanium alloys of Nos. 40′ and 41′. This is because the test specimensmade of the titanium alloys of Nos. 40′ and 41′ have a thickness of anoxygen compound layer of less than 20 nm, whereas the test specimensmade of titanium alloys of Nos. 36 to 43 have a thickness of the oxygencompound layer of 20 nm or more.

Further, the test specimens made of the titanium alloys of Nos. 36-43have larger seizure load compared with the test specimen made of thetitanium alloy of No. 37′. This is because the test specimen made of thetitanium alloy of No. 37′ has a thickness of the oxygen compound layerof 110 nm, whereas the test specimens made of the titanium alloys ofNos. 36-43 have an oxygen compound layer with a thickness of 95 nm orless.

From the foregoings, it can be seen that the wear resistance of thebearing ring made of the titanium alloy can be increased by forming theoxide compound layer containing TiO_(x) to the surface of the bearingring made of the titanium alloy. Further, it can be seen that the wearresistance of the bearing ring made of the titanium alloy can beincreased further by making the thickness of the oxide compound layer to20 nm or more and 95 nm or less.

FIG. 8 shows a relation between the thickness of the oxide compoundlayer and the maximum wear indentation depth of the test specimen madeof the titanium alloy shown in Table 5. As shown in the figure, as thethickness of the oxygen compound layer is 20 nm or more, the maximumwear indentation depth is about 2 μm or less and as the thickness of theoxygen compound layer is 50 nm or more, the maximum wear indentationdepth is about 1 μm or less. Accordingly, the wear resistance of thebearing ring made of the titanium can be increased further by definingthe thickness of the oxygen compound layer to 20-95 nm, preferably,50-95 nm.

Rolling Life Test

Bearing rings were manufactured with materials shown in Table 6, whichwere incorporated into test bearings in which the rolling elementcomprised Si₃N₄ and the cage comprised a fluoro resin, and a rollinglife test in water for rolling bearing was conducted under theconditions at radial load: 98 N, axial load: 20 N, rotational speed:1000 rpm and in a lubrication state: no lubrication.

Table 6 shows the rolling life for each of the test bearings obtained bythe rolling life test in water. The rolling life ratios in Table 6 arecomparative values in a case of evaluation based on the rolling life ofNo. 44′ being assumed as 1.

TABLE 6 Compound Kind of layer Core Rolling Material for test Oxidationcompound thickness hardness life No. specimen condition (0 < x < 2) (nm)(Hv) ratio Example 36 Ti-6Al-4V 500° C. × 40 h TiO₂, TiOx 75 455 3.0 37Ti-6Al-4V 550° C. × 20 h TiO₂, TiOx 80 429 3.2 38 Ti-6Al-4V 600° C. × 10h TiO₂, TiOx 95 421 2.8 39 Ti-15V-3Cr-3Sn-3Al 475° C. × 50 h TiO₂, TiOx65 430 3.1 40 Ti-22V-4Al 475° C. × 50 h TiO₂, TiOx 70 441 2.9 41Ti-15Mo-5Zr-3Al 400° C. × 60 h TiO₂, TiOx 25 467 3.5 42 Ti-15Mo-5Zr-3Al450° C. × 60 h TiO₂, TiOx 55 503 3.2 43 Ti-15Mo-5Zr-3Al 500° C. × 60 hTiO₂, TiOx 90 452 3.5 Comp. 36′ Ti-6A1-4V Only aging — 0 429 1.6 Example37′ Ti-6Al-4V 600° C. × 20 h TiO₂, TiOx 110 411 2.1 38′ Ti-6Al-4V 700°C. × 20 h TiO₂ 1800 373 1.9 39′ Ti-22V-4Al Only aging — 0 480 1.7 40′Ti-15Mo-5Zr-3Al 400° C. × 20 h TiO₂, TiOx 15 448 1.9 41′ Ti-15Mo-5Zr-3Al300° C. × 40 h TiO₂, TiOx 10 384 1.4 42′ SUS630 — — 0 465 1.4 43′ YHD50— — 0 432 1.2 44′ Be—Cu — — 0 418 1.0

As can be seen from the test results in Table 6, the test bearings Nos.36-43 show larger values for the rolling life ratio compared with thetest bearings Nos. 36′ and 39′. This is because the oxide compound layeris not formed on the surface of the bearing rings made of the titaniumalloys in the test bearings Nos. 36′ and 39′, whereas the oxide compoundlayer is formed on the surface of the bearing rings made of the titaniumalloys in the test bearings Nos. 36-43. Further, the test bearings Nos.36-43 show larger values for the rolling life ratio compared with thetest bearings No. 38′. This is because the oxygen compound layer doesnot contain TiO_(x) (0<x<2) in the test bearings No. 38′, whereas theoxygen compound layer contains TiO_(x) (0<x<2) in the test bearings Nos.36-43. Further, the test bearings Nos. 36-43 are excellent in therolling life compared with the test bearings Nos. 40′ and 41′. This isbecause the thickness of the oxygen compound layer is less than 20 nm inthe test bearings of Nos. 40′ and 41′, whereas the thickness of theoxygen compound layer is 20 nm or more in the test bearings Nos. 36-43.

FIG. 9 shows a relation between the rolling life ratio for each of thetest bearings and the core hardness of the rolling bearings made of thetitanium alloys shown in Table 6. As shown in the figure, the rollinglife of the bearing is about 2.0 as the comparative value when the corehardness of the bearing ring made of the titanium alloy is less than Hv420, whereas the rolling life of the bearing is about 3.5 as thecomparative value when the core hardness of the bearing ring made of thetitanium alloy is Hv 420 or more. Accordingly, it can be seen that therolling life of the rolling bearing can be increased by increasing thecore hardness of the bearing ring made of the titanium alloy to Hv 420or more.

Then, test specimens were manufactured with materials shown in Table 7and a solution treatment and an aging treatment were applied to the testspecimens Nos. 1-14 under the conditions shown in the table. Then, usingthe test specimens, measurement for the particle diameter of theω-phase, Vickers' hardness test, salt spray test and Sawin type weartest were conducted.

TABLE 7 No. Kind of alloy Solution condition Aging condition 1 Ti-6Al-4VWater cooling after keeping Air cooling after keeping 10 hr at 420° C. 1hr at 950° C. 2 Ti-15Mo-5Zr-3Al Water cooling after keeping Air coolingafter keeping 50 hr at 350° C. 1 hr at 800° C. 3 Ti-15Mo-5Zr-3Al Watercooling after keeping Air cooling after keeping 15 hr at 400° C. 1 hr at800° C. 4 Ti-15Mo-5Zr-3Al Water cooling after keeping Air cooling afterkeeping 10 hr at 450° C. 1 hr at 800° C. 5 Ti-15Mo-5Zr-3Al Water coolingafter keeping Air cooling after keeping 10 hr at 475° C. 1 hr at 800° C.6 Ti-15Mo-5Zr-3Al Water cooling after keeping Air cooling after keeping50 hr at 450° C. 1 hr at 780° C. 7 Ti-15Mo-5Zr-3Al Water cooling afterkeeping 50% cold rolling, keeping at 475° C. for 7 hr and 1 hr at 800°C. then furnace cooling 8 Ti-15Mo-5Zr-3Al Water cooling after keeping70% cold rolling, keeping at 475° C. for 7 hr and 1 hr at 800° C. thenfurnace cooling 9 Ti-15V-3Cr-3Sn- Water cooling after keeping Aircooling after keeping 15 hr at 400° C. 3Al 1 hr at 800° C. 10Ti-15V-3Cr-3Sn- Water cooling after keeping Air cooling after keeping 10hr at 450° C. 3Al 1 hr at 800° C. 11 Ti-15V-3Cr-3Sn- Water cooling afterkeeping Air cooling after keeping 7 hr at 500° C. 3Al 1 hr at 800° C. 12Ti-15V-3Cr-3Sn- Water cooling after keeping Air cooling after keeping100 hr at 450° C. 3Al 1 hr at 800° C. 13 Ti-15V-3Cr-3Sn- Water coolingafter keeping Air cooling after keeping 0.1 hr at 400° C. 3Al 1 hr at800° C. 14 SUS440C Oil cooling after keeping keeping 2 hr at 170° C.(tempering) 1 hr at 1050° C. 15 Be—Cu No solution treatment Air coolingafter keeping 2 hr at 350° C.

Particle Diameter Measurement for ω-Phase

Crystal tissue for the cross section of a test specimen was observed fordark view images using a test specimen for transmission type electronmicroscopic observation by using a transmission type electron microscope“JEM-2010” manufactured by Nippon Denshi Co. to measure the particlediameter for the ω phase. As a result of the observation, the crystaltissue of the titanium alloy was (β+ω) phase or (β+ω+α) in Nos. 1-10 and13 and (β+α) phase in No. 11.

Vickers Hardness Test

After mirror-polishing the cross section of a test specimen, it wasmeasured under the conditions at a load of 100 g by a micro Vickershardness tester while abutting a presser to the mirror face of the testspecimen.

Salt Water Spray Test

According to “JIS Z2371”, and using an aqueous NaCl solution at 5% byweight concentration at a temperature of 35° C., the appearance of thetest specimen after lapse of one week was observed visually. Those notrecognized for the occurrence of rust was evaluated as havingsatisfactory corrosion resistance (∘) and those recognized for theoccurrence of rust was evaluated as having poor corrosion resistance (X)by the observation.

Sawin Type Wear Test

As shown in FIG. 11A and FIG. 11B, a fixed test specimen 21 comprisingvarious kinds of alloys manufactured as described above and a rotationaltest specimen 22 comprising Si₃N₄ were attached to a Sawin type weartester and the rotational test specimen 22 was rotated relative to thefixed test specimen 21 without lubrication while pressing the fixed testspecimen 21 to the outer circumferential surface of the rotational testspecimen 22 by a weight for loading and a weight for balancing. Thefixed test specimen 21 is sized 19 mm×19 mm×3 mm thickness, while thering-shaped rotational test specimen 22 is sized 45 mm: outer diameter,6 mm: thickness and 6 mm: width.

The conditions for the rotation were at a pressing load of 39.2 N, at arotational speed of the rotational test specimen 22 to the fixed testspecimen 21 of 2.6 m/s as the circumferential speed and for a rotationaldistance of the rotational test specimen 22 of 400 m. The wear volume ofthe test specimen 21 along with rotation was measured and the ratio whenassuming the wear volume of No. 11 as 1 was calculated as “wear ratio”for each of the specimens.

Table 8 shows the test results.

TABLE 8 ω phase particle Hardness Wear Corrosion No. diameter (Hv) ratioresistance 1 1 μm or less 492 0.72 ◯ 2 1 μm or less 514 0.64 ◯ 3 1 μm orless 520 0.68 ◯ 4 1 μm or less 510 0.72 ◯ 5 1 μm or less 493 0.69 ◯ 6 1μm or less 491 0.65 ◯ 7 1 μm or less 530 0.61 ◯ 8 1 μm or less 528 0.60◯ 9 1 μm or less 501 0.72 ◯ 10 1 μm or less 492 0.68 ◯ 11 No ω phase 4531.0 ◯ 12 1 μ over 430 1.4 ◯ 13 10 nm or less 480 0.88 ◯ 14 — 690 0.1 X15 — 421 2.3 ◯

As can be seen from the test result of Table 8, Nos. 1 to 10 and No. 13corresponding to the examples of the present invention are moreexcellent in the wear resistance and favorable in the corrosionresistance by the use of a titanium alloy of a crystal tissue having theω phase with the particle diameter of 1 μm or less, compared with a caseof using a titanium alloy of a crystal tissue not having ω phase (No.11), a case in which the particle diameter of the ω phase exceeds 1 μm(No. 12) and a case of using the Be—Cu alloy (No. 15). In a case ofusing stainless steel (No. 14), the hardness and the wear resistancewere favorable but the corrosion resistance in salt water was poor.

In No. 5, the temperature for the aging treatment is 475° C., which ishigher than the ω phase precipitation temperature and it is consideredthat the ω phase precipitated in a temperature region from 300 to 450°C. during cooling to form a (β+ω+α) phase since the cooling rate afterthe aging treatment was lowered by gradual cooling in the furnace.

In Nos. 7 and 8, since a great amount of plastic strains are introducedby cold rolling into the titanium alloy, a number of nuclei of theω-phase are formed during gradual cooling to increase the existent ratioof the ω-phase in the titanium alloy (volume ratio) compared with thecase of not applying cold rolling (No. 5). Thus, the hardness wasincreased and the wear resistance was also preferred particularly.

In No. 13, since the particle diameter of the ω phase was relativelysmall as 10 nm or less, the hardness and the wear resistance weresomewhat inferior to those of Nos. 1 to 10, but it was within a rangethat is usable as bearing rings or rolling elements of rolling bearings.

From the foregoings, in the rolling bearing comprising the inner ring(raceway member) 2, the outer ring, (raceway member) 1, the rollingelements 3 and the cage 4, the inner ring 2 and the outer ring 1comprising the titanium alloy of the crystal tissue having the ω phasewith a particle diameter of 1 μm or less are obtained by manufacturingthe inner ring 2 and the outer ring 1 in the same manner as for testspecimens of Nos. 1 to 10 and 13. Then, by the combination of the innerring 2 and the outer ring 1 with the rolling elements 3, for example,made of ceramics such as Si₃N₄ and, optionally, the cage 4, for example,made of plastics, a rolling bearing suitable to use in a corrosivecircumstance or a circumstance requiring non-magnetic property can beobtained.

FIG. 12 is a cross sectional view of a deep groove ball bearing (bearingnumber: 608) as another embodiment of the present invention. In thedrawing, the outer ring 1 and the inner ring 2 are formed of α+β typetitanium alloy such as Ti-6Al 4V or α+β type titanium alloy such asTi-15Mo-5Zr-3Al, Ti-15Mo-5Zr-3Al and the like. The rolling element 3disposed between the outer ring 1 and the inner ring 2 is formed ofceramics such as silicon nitride, silicon carbide, zirconia and alumina.A hard film 6 is formed to the raceway surface of the bearing rings 1and 2 along which the rolling elements 3 roll. The hard film comprises,for example, TiN, CrN, TiAlN or diamond-like carbon and a lubricatingfilm 7 comprising a fluoro-containing a molybdenum disulfide, tungstensulfide or fluoro-containing polymer having functional groups is formedon the surface of the hard film 6.

The titanium alloy is applied with a hardening treatment by a first orsecond method after machining into a predetermined shape for obtaining ahardness of Hv 350 or more by Vickers hardness.

The first method is a method of applying a solution treatment and anaging treatment to the titanium alloy to obtain a hardness of Hv 350 ormore and the second method is a method of applying a gas nitridationtreatment to the titanium alloy to obtain a hardness of Hv 350 or more.

In the first method, in a case where the titanium alloy is Ti-6Al-4V,the titanium alloy is placed in a temperature atmosphere at 950 to 1000°C. for one hour and, subsequently, the titanium alloy is water cooled toapply a solution treatment. Further, in a case where the titanium alloyis Ti-15Mo-5Zr-3Al or Ti-15Mo-5Zr-3Al, the titanium alloy is placed in atemperature atmosphere from 800 to 850° C. for about one hour and,subsequently, the titanium alloy is water cooled to apply a solutiontreatment.

In a case of precipitating the α phase of high hardness from the β phaseof the titanium alloy, after the solution treatment, the titanium alloyis placed in a temperature atmosphere of 300 to 500° C. for about 3 to40 hours to apply an aging treatment to the titanium alloy. The hardnessof the titanium alloy is adjusted by controlling the time for the agingtreatment. Cooling of the titanium alloy by the aging treatment isusually conducted by air cooling and for making the hardness of thetitanium alloy harder, it is desirable to gradually cool the titaniumalloy in the furnace in order to more finely precipitate the α phasefrom the β phase.

In a case of obtaining a hardness of Hv 350 or more by the secondmethod, The titanium alloy is heated in a furnace under vacuum at atemperature lower than the transformation point in order to preventoxidation on the surface of the titanium alloy. In this case, when thepressure in the furnace, exceeds 0.133 Pa, residual oxygen in thefurnace and titanium react chemically to form an oxide layer on thesurface of the titanium alloy that hinders the nitridation treatment.Accordingly, in a case of obtaining a hardness of Hv 350 or more by thenitridation treatment of the titanium alloy, the pressure in the furnaceis lowered to 0.133 Pa or less as shown in FIG. 13.

When the nitridation treatment temperature for the titanium alloy ishigh, reactivity between titanium and nitrogen is favorable. Thediffusion rate of nitrogen intruding into the titanium alloy increasestherealong and, as a result, a nitrogen diffusion layer is formed to thesurface of layer of the titanium alloy. However, when the nitridationtreatment temperature is higher than the transformation point(temperature from α phase to β phase) or higher, crystal grains growabruptly to give undesired effects on the fatigue strength of thebearing ring. Accordingly, when the titanium alloy is nitrided with atreating gas such as a nitrogen gas or NH₃, the nitridation treatmenttemperature is controlled to a temperature lower by about 5 to 200° C.than the transformation point.

In a case of nitriding the titanium alloy with a treating gas such as anitrogen gas or NH₃, when the pressure of the treating gas isexcessively high, nitridation on the surface of the titanium alloyproceeds rapidly to make the nitride layer formed on the surface of thetitanium alloy coarse and brittle. In order to avoid this, it isdesirable to control the gas pressure in the furnace to 1333 Pa or less.Further, also during cooling, it is desirable to conduct cooling in thefurnace while keeping a predetermined gas pressure in order to preventoxidation.

Then, a method of forming the hard film 6 to the raceway surface of theouter ring 1 and the inner ring 2 is to be explained.

The hard film 6 was formed by using a film deposition treatmentapparatus utilizing an arc vapor deposition method (refer to FIG. 14).Specifically, a test bearing was placed on a turn table 42 having arotational shaft 47. Then, the inside of a vacuum vessel 41 wasevacuated by a vacuum pump 46 to condition the pressure to 1×10⁴ Pa orless, under which DC bias was applied to a pair of cathodes 43 and 43while introducing an Ar gas from a gas introduction port 44 to apply ionbombarding by Ar and apply cleaning for a work 48 (outer ring 1 andinner ring 2).

Then, the temperature of the work 48 was elevated to 400 to 500° C. anda Ti material in a case of forming a Ti series hard film 6 or a Crmaterial in a case of forming a Cr film hard film 6 are attached,respectively, to targets 49 and 50. Then, while rotating the turn table42, a bias at −200 to −300 V, 80 to 150 A was applied to the targets 49and 50.

Further, a nitrogen gas was introduced as a treating gas in a case offorming the nitride type hard film 6 or a methane gas (CH₄) wasintroduced as a treating gas in a case of forming the carbide type film6 from the gas introduction port 45 and an identical DC bias was appliedto the targets 49 and 50 while rotating the turn table 42.

By the procedures described above, the hard film 6 could be formed atleast on the entire inner circumferential surface of the outer ring 1and at least on the entire outer circumferential surface of the innerring 2. The thickness of the hard film 6 was controlled by the treatmenttime. For those applied with the gas nitridation treatment, the nitrogencompound layer formed on the surface by the gas nitridation treatmentwas removed by finish polishing to expose the nitrogen diffusion layerto condition the surface hardness to Hv 550 or more, and a hard film 6was formed to the upper layer thereof.

The method of forming the hard film 6 is not restricted to the method asdescribed above but, for example, an HCD ion plating method, sputteringmethod, plasma CVD method or the like may be adopted.

Then, the result of evaluation for the peeling life of the hard film isto be explained. Bearings used were thrust ball bearings manufactured bythe same method as described above (bearing No.: 51305).

As shown in FIG. 15, a thrust ball bearing 12 comprising an outer ring1, an inner ring 2, rolling elements 3 and a cage 4 was attached to arotational shaft 51 of a thrust life testing machine and a rotation testwas conducted in a state of filling a lubricant in a housing 53 underthe conditions at a load of 9800 N, a rotational speed of 1000 rpm,using brass as the material of the cage, silicone nitride as thematerial of roiling element and #68 turbine oil (68 cSt/40° C.) as thelubricant.

Table 9 shows the surface hardness Hv for the base material of the outerring 1 and the inner ring 2, the kind of the hard film and the result ofpeeling life, respectively.

TABLE 9 Type of base Hardness of Peeling material base material Hardlife No. hardening surface film ratio Example  1 A 450 TiN 33  2 A 500TiN 52  3 A 500 TiAlN 78  4 A 500 SiC + DLC 45  5 B 603 TiN 85  6 B 889TiN 83  7 B 889 TiAlN 132  8 B 889 SiC + DLC 111  9 A 376 TiN 10.5 10 A376 TiAlN 13.2 11 A 350 TiN 8.5 12 A 350 TiAlN 10.1 Comp.  3′ None 290TiN 1 Example  4′ A 290 TiAlN 1.8 A: Solution treatment + age hardeningtreatment B: Gas nitridation

The base material for the outer ring 1 and the inner ring 2 in Table 9is β type titanium alloy: Ti-15Mo-5Zr-3Al. For the judgment of thepeeling life, the instance at which a vibration level detected by anacceleration pick up reached five times the initial value was defined asthe life. Then, it is indicated as a comparative value based on the lifeof a raw material (base material not applied with hardening treatment)covered with a hard film comprising TiN (No. 1′ in Table 9) beingassumed as 1.

FIG. 16 shows a relation between the surface hardness Hv of the basematerial and the peeling life of the hard film is shown. As can be seenfrom FIG. 16, when the surface hardness of the base material is Hv 350or more, the peeling life of the hard film is improved and it wasfurther improved at Hv 450 or more.

As can be seen from Table 9 and FIG. 16, Nos 1 to 12 corresponding tothe examples of the present invention show larger values for the peelinglife ratio of the hard film compared with No. 3′ and No. 4′ as thecomparative examples. This is because the surface hardness of theraceway surface formed with the hard film is Hv 290 or less in thebearings No. 31 and No. 4′, whereas the surface hardness of the racewaysurface formed with the hard film is Hv 350 or more in the bearings Nos.1 to 12.

Comparing Nos. 1 to 4 with Nos. 9 to 12 shown in Table 9, it can be seenthat the peeling life ratio of Nos. 1 to 4 shows larger values than thepeeling life ratio of Nos. 9 to 12. This is because the surface hardnessof the raceway surface is Hv 376 or less in the bearings Nos. 9 to 12,whereas the surface hardness of the raceway surface is Hv 450 or more inthe bearings Nos. 1 to 4.

Accordingly, durability of the hard film can be improved and earlypeeling or the like of the hard film can be prevented by increasing thesurface hardness of the raceway surface formed with the hard film to Hv350 or more preferably, Hv 450 or more.

Then, the result for the evaluation of the durability of rolling bearingin a vacuum atmosphere is to be explained. The bearing used is a deepgroove ball bearing manufactured by the same method as described above(bearing number: 608, inner diameter 8 mm×outer diameter 22 mm×width 7mm).

A deep groove ball bearing having an outer ring 1, an inner ring 2 androlling elements 3 was attached in a bearing housing 62 in a vacuumchamber 61 of a vacuum duration test apparatus (refer to FIG. 17) andduration test under vacuum atmosphere was conducted. Rotation of a motor63 is introduced by way of a magnetic seal unit 64 to the test bearing10. Further, the axial load is applied by a coil spring 65 to the testbearing 10 and the rotational torque of the test bearing 10 is measuredby a leaf spring appended with a not illustrated strain gage. Further,inside of the vacuum chamber 61 is evacuated by a not illustrated turbomolecular pump and an ion pump.

The test conditions in this case are as shown below;

Axial load 49 N Rotational speed 1000 Rpm Vacuum degree 10⁻⁵ Pa or less

Table 10 shows the kind of the base material for the outer ring 1 andthe inner ring 2, the type of the hardening treatment applied to thebase material, the surface hardness Hv of the base material, the kind ofthe hard film 6, the kind of the lubricating film 7, the material forthe rolling element 3 and the life (result of vacuum duration test),respectively. “DFO” in the column for the kind of the lubricating filmmeans a fluoro-containing polymer having functional groups. Further, thelife was indicated by a relative value based on the life of a rawmaterial (base material not applied with hardening treatment) coveredwith a hard film comprising TiN (No. 3′ in Table 10) being assumed as 1.

TABLE 10 Hardness of base Material for base material Kind of Kind ofMaterial of Life No. material Hardening Hv hard film lubricant filmrolling element ratio Example 13 Ti-6Al-4V B 554 TiN DFO Silicon nitride42 14 Ti-15Mo-5Zr-3Al A 450 TiN DFO Silicon nitride 48 15Ti-15Mo-5Zr-3Al B 603 CrN DFO Silicon nitride ≧100 16 Ti-15Mo-5Zr-3Al B603 TiAlN DFO Silicon nitride ≧100 17 Ti-15Mo-5Zr-3Al B 603 DLC DFOSilicon nitride ≧100 18 Ti-15Mo-5Zr-3Al B 603 TiN DFO Zirconia ≧100 19Ti-15Mo-5Zr-3Al B 603 TiN DFO Silicon carbide ≧100 20 Ti-15Mo-5Zr-3Al B603 TiN DFO Alumina ≧100 21 Ti-15Mo-5Zr-3Al B 603 TiN DFO 2) ≧100 22Ti-15Mo-5Zr-3Al B 603 DLC MoS₂ Silicon nitride 35 23 Ti-15Mo-5Zr-3Al B603 DLC WS₂ Silicon nitride 41 24 Ti-15Mo-5Zr-3Al B 603 DLC None Siliconnitride 22 25 Ti-15Mo-5Zr B 667 TiN DFO Silicon nitride ≧100 26Ti-15Mo-5Zr A 552 TiN DFO Silicon nitride ≧100 27 Ti-15Mo-5Zr-3Al A 376TiN DFO Silicon nitride 33 28 Ti-15Mo-5Zr-3Al A 376 TiN MoS₂ Siliconnitride 18 29 Ti-15Mo-5Zr-3Al A 376 TiN WS₂ Silicon nitride 19  3′Ti-15Mo-5Zr-3Al None 290 TiN DFO Silicon nitride 1  4′ Ti-15Mo-5Zr-3Al B603 None DFO Silicon nitride 7.6 1) A: Solution treatment + agehardening treatment B: Gas nitridation treatment 2) Silicon nitride +TiN film

As can be seen from Table 10, Nos. 13 to 29 corresponding to theexamples of the present invention show larger values for the life ratiocompared with No. 3′ as the comparative example. This is because thesurface hardness of the raceway surface is Hv 290 or less in bearing No.3′, whereas the surface hardness is Hv 350 or more for the racewaysurface in bearings Nos. 13 to 29. Further, Nos. 13 to 29 correspondingto the examples of the present invention show larger values for the liferatio in vacuum compared with No. 4′ as the comparative example. This isbecause a lubricating film is formed directly on the raceway surface ofa bearing ring made of the titanium alloy in bearing No. 4′, whereas thelubricating film is formed on the surface of the hard film formed on theraceway surface in the bearing Nos. 13 to 29.

Accordingly, it can be seen that a rolling bearing that can be usedfavorably for a long period of time even under a vacuum atmosphere wherea lubricant such as grease can not be used can be obtained by formingthe hard film on the raceway surface of the bearing ring made of thetitanium alloy and forming the lubricant film on the surface of the hardfilm.

As the base material, Ti-6Al-4V of α+β type titanium alloy andTi-15Mo-5Zr-3Al and Ti-15Mo-5Zr of β type titanium alloy are used, butthe kind of the titanium alloys is not restricted to those describedabove and other kinds of titanium alloys may also be used so long as thesurface hardness of the base material can be Hv 350 or more, preferably,Hv 450 or more.

Table 11 shows the conditions for the solution treatment and theconditions for the aging treatment for the bearing rings made oftitanium alloys.

TABLE 11 Aging Material for Solution treatment treatment Symbol bearingring condition condition A Ti-15Mo-5Zr-3A1 730-850° C. × 1 Hr 450° C. ×20 Hr B ↑ 800-850° C. × 1 Hr 450° C. × 20 Hr 475° C. × 10 Hr CTi-15Mo-5Zr 730-850° C. × 2 Hr 400° C. × 90 Hr D ↑ 730-850° C. × 2 Hr450° C. × 20 Hr E Ti-15V-3Cr-3Sn-3A1 730-850° C. × 3 Hr 450° C. × 20 HrF Ti-22V-4A1 730-850° C. × 4 Hr 450° C. × 20 Hr G Ti-6A1-4V 900° C. × 1Hr 540° C. × 10 Hr

Vacuum Rotation Test

Test bearings were manufactured by using bearing rings made of titaniumalloys shown in Table 11 and rolling elements made of materials shown inTable 12 and a wear resistance test was conducted for each of the testbearings under vacuum. Specifically, the rotation test was conducted invacuum for each of the test bearings under the conditions at an axialload of 19.6 N and at a rotational speed of 1000 rpm and in alubrication state of no lubrication, and the amount of wear in each ofthe bearing rings after 1×10⁷ rotation was calculated as [wear ratio]based on the ratio defining the amount of wear in No. 1′ being assumedas 1.

Table 12 shows the test result of the vacuum rotation test.

TABLE 12 heat conductivity No. Inner/outer ring Material for rollingelement (W/m · K) Wear ratio of bearing ring Example  1 B WC-6% Co 620.42  2 B WC-6% TiC-13% TaC-6% Co 50 0.45  3 B TiC-20% TiN-15% WC-10%Mo₂C-5% Ni 35 0.52  4 B TiC-25% TiN-15% WC-5% Mo₂C-15% Ni 51 0.42  5 BWC-6% TiC-13% TaC-6% Co 43 0.48  6 A WC-6% TiC-13% TaC-6% Co 50 0.47  7C WC-6% TiC-13% TaC-6% Co 50 0.44  8 D TiC-20% TiN-15% WC-10% Mo₂C-5% Ni35 0.62  9 E TiC-20% TiN-15% WC-10% Mo₂C-5% Ni 35 0.63 10 F WC-6%TiC-13% TaC-6% Co 43 0.54 11 G WC-6% TiC-13% TaC-6% Co 43 0.51 Comp.  1′C Si₃N₄ 31 1.00 Example  2′ C WO-2% TaC-15% Co 32 0.91  3′ C TiC-20%TiN-15% WC-12% Mo₂C-15% Ni 29 0.82

The wear ratio for each of the bearing rings shown in Table 12 is acomparative value in a case of evaluation based on the wear amount ofNo. 1′ being assumed as 1.

As can be seen from the test result of Table 12, Nos. 1 to 12corresponding to the examples of the present invention show largervalues for the life ratio compared with No. 1′ as the comparativeexample. This is because the material for the rolling element of therolling bearing No. 1′ is SiN₄, whereas the material for the rollingelement of the rolling bearings Nos. 1 to 12 is superhard alloy orcermet.

Further, the bearings Nos. 1 to 12 show larger values for the life ratiocompared with No. 2′ and No. 3′ as the comparative examples. This isbecause the heat conductivity of the superhard alloy or cermet of thebearings No. 2′ and No. 3′ is 31 W/(m·K) or less, whereas the heatconductivity of the superhard alloy or cermet of the rolling bearingsNos. 1 to 12 is 35 W/(m·K) or more.

Accordingly, it can be seen that rolling bearings that can be usedfavorably for a long period of time even under a vacuum atmosphere canbe obtained by forming the rolling element of the superhard alloy orcermet and increasing the heat conductivity of the superhard alloy orcermet to 35 W/(m·K) or more.

FIG. 18 shows a relation between the wear ratio shown in Table 12 andthe heat conductivity of the superhard alloy or cermet. As shown in thefigure, the wear ratio of the bearing ring made of the titanium alloyincreases as the heat conductivity of the superhard alloy or cermet ishigher till the heat conductivity reaches 50 W/(m·K), but the wear ratioof the bearing ring made of titanium does not increase so much even whenthe heat conductivity of the superhard alloy or the cermet increase whenthe heat conductivity exceeds 50 W/(m·K).

From the foregoings, it is desirable to set the heat conductivity of thesuperhard alloy or cermet within a range from 30 to 50 W/(m·K) in a caseof forming the rolling element of the superhard alloy or cermet.

Rolling bearings for test were manufactured with the materials shown inTable 13 and the following salt water rolling test and a magnetic fluxdensity change measuring test were conducted to each of the thusmanufactured test bearings. In Table 13, the materials A, B, C and G forthe bearing rings are materials shown in Table 11 and NR8 is WC-Niseries superhard alloy, NR 11 is WC—Ni—Cr series superhard alloy and DUX30 is TiC—TaN—Ni—Mo series cermet as the material for the rollingelement.

TABLE 13 Rolling test in salt Material for Heat conductivity waterChange of Material for rolling of rolling element Bearing ring magneticflux No. bearing ring element (W/m · K) wear ratio rusting densityExample 12 A Superhard 75 0.38 No No alloy NR8 13 B ↑ ↑ 0.35 No No 14 C↑ ↑ 0.31 No No 15 D ↑ ↑ 0.35 No No 16 G ↑ ↑ 0.41 No No 17 A Superhard 630.40 No No alloy NR11 18 B ↑ ↑ 0.36 No No 19 C ↑ ↑ 0.31 No No 20 D ↑ ↑0.38 No No 21 G ↑ ↑ 0.44 No No 22 A Cermet DUX30 35 0.50 No No 23 B ↑ ↑0.43 No No 24 C ↑ ↑ 0.49 No No 25 D ↑ ↑ 0.45 No No 26 G ↑ ↑ 0.61 No NoComp. 4′ B Si₃N₄ 31 1.0  No No Example

Rolling Test in Salt Water

Using the test apparatus shown in FIG. 2, a rolling life test in anaqueous NaCl solution at 5 wt % concentration was conducted for each oftest bearings to examine the wear ratio and presence or absence ofrusting in each of bearing rings. The test conditions in this case areas shown below;

Radial Load 49.2 N Axial load 19.2 N Rotational speed 1000 rpmLubrication no lubrication

Magnetic Flux Density Change Measuring Test

As shown in FIG. 5, after attaching a test bearing 10 to a rotationalshaft 13 rotated in a magnetic field of a permanent magnet 16, therotational shaft 13 was rotated at a speed of about 500 rpm and thechange of the magnetic flux density was measured by a tesla meter 17.Then, those showing the output of the tesla meter of 0.1 Mt or more atthe maximum were defined as with change of the magnetic flux density andthose showing less than 0.1 Mt were defined as with no change of themagnetic flux density. Table 13 shows the test result. As can be seenfrom the test result in the table, Nos. 1 to 26 corresponding to theexamples of the present invention showed excellent wear resistance evenunder corrosive circumstance in salt water and of course no rusting wasobserved. Further, since there was no change of the magnetic fluxdensity at all, it was confirmed that they were excellent also in viewof non-magnetic property.

Since the superhard alloy or cermet has high hardness (Hv 900 or more)and high melting point corresponding to ceramics, they cause lessadhesion or wear even if the lubricating condition is stringent.Further, since they have high hardness, the amount of plasticdeformation during working is very small and a small degree ofunevenness is less caused. Therefore, rolling elements at an extremelyhigh accuracy can be manufactured. Further, with respect to thetoughness, since it is higher than that of ceramics, cracking orchipping is less caused during manufacture and they are less fracturedagainst impact load.

By the use of the superhard alloy or cermet having the heat conductivityof 35 W/(m·K) or more as the material for the rolling element, theamount of heat generation at the face of contact between the bearingring and the rolling element can be suppressed to suppress the adhesivewear of the bearing ring made of titanium alloy. Further, since thesuperhard alloy or cermet has a larger Young' modulus compared withceramics, the area of contact between the rolling element and thebearing ring is reduced, so that the rotational torque can be suppressedto stabilize the rotational characteristics.

The superhard alloy and the cermet are alloys formed of nine kinds ofmetals belonging to the group IVa, the group Va and the group VIa of theperiodical table, namely, W, Mo, Cr, Ta, Nb, V, Hf, Zr and Ti as targetsby sinter bonding the powder of such carbides by using iron group metalssuch as Fe, Co and Ni. The cermets are sintered alloys formed by bondingmainly TiC, TiN or TiCN, among them, with Ni.

The superhard alloys when classified in accordance with alloy systems,include, for example, WC—Co series, WC—Cr₃C₂—Co system, WC—TaC—Cosystem, WC—TiC—Co series, WC—NbC—Co system, WC—TaC—NbC—Co series,WC—TiC—TaC—NbC—Co series, WC—TiC—TaC—Co series, WC—ZrC—Co series,WC—TiC—ZrC—Co series, WC—TaC—VC—Co series, WC—Cr₃C₂—Co series andWC—TiC—Cr₃C₂—Co series. Those improved with the corrosion resistanceinclude, for example, WC—Ni series, WC—Co—Ni series, WC—Cr₃C₂—Mo₂C—Niseries, WC—Ti(C,N)—TaC series, WC—Ti(C,N) series and Cr₃C₂—Ni series.

A typical composition for the WC-Co series comprisesW:Co:C=70.41-91.06:3.0-25.0:4.59-5.94. A typical composition ofWC—TaC—NbC—Co series comprisesW:Co:Ta:Nb:C=65.7-86.3:5.8-25.0:1.4-3.1:0.3-1.5:4.7-5.8. A typicalcomposition of the WC—TiC—TaC—NbC—Co series comprisesW:Co:Ta:Ti:Nb:C=65.0-75.3-6.0-10.7:5.2-7.2:3.2-11.0:1.6-2.4:6.2-7.6. Atypical composition for the WC—TaC—Co series comprisesW:Co:Ta:C=53.51-90.30:3.5-25.0:0.30-25.33:4.59-5.90. A typical exampleof the WC—TiC—Co series compriseW:Co:Ti:C=57.27-78.86:4.0-13.0:3.20-25.59:5.88-10.14. A typical examplefor the WC—TiC—TaC—Co comprisesW:Co:Ta:Ti:C=47.38-87.31:3.0-10.0:0.94-9.38:0.12-25.59:5.96-10.15.

The cermets include, for example, TiC—Ni series, TiC—Mo—Ni series,TiC—Co series, TiC—MO₂C—Ni series, TiC—Mo₂C—ZrC—Ni series, TiC—MO₂C—Coseries, Mo₂C—Ni series Ti(C, N)—MO₂C—Ni series, TiC—TiN—Mo₂C—Ni series,TiC—TiN—MO₂C—Co series, TiC—TiN—Mo₂C—TaC—Ni series,TiC—TiN—Mo₂C—WC—TaC—Ni series, TiC—WC—Ni series, Ti(C,N)—WC—Ni series,TiC—Mo series, and Ti(C, N)—Mo series. Ti(C,N)—MO₂C—Ni series,Ti(C,N)—WC—Ni series or Ti(C,N)—Mo series is an alloy formed bysintering TiC—Mo₂C—Ni series, TiC—WC—Ni series or TiC—Mo series in anitrogen gas (N₂).

The typical composition of the cermet comprises, for example, TiC-30%Ni, TiC-10% Mo-30% Ni, TiC-20% Mo-30% Ni, TiC-30% Mo-30% Ni, TiC-11%MO₂C 11% Mo₂C-24% Ni, TiC-30% MO₂C-20% Ni, TiC-19% Mo₂C-24% Ni, TiC-8%Mo₂C-15% Ni, Ti(C,N)-25%Mo₂C-15%, TiC-14% TiN-19% Mo₂C-24% Ni,TiC_(0.7)N_(0.3-11)% Mo₂C-24% Ni, TiC_(0.7)N_(0.3-19)% Mo₂C-24% Ni,TiC_(0.7)N_(0.3-27)% Mo₂C-24% Ni, TiC-20% Mo-15% Ni, TiC-30% Mo-15% Ni.

High resistance and non-magnetic property can be coped with by thechange of the ingredient systems of the superhard alloy or cermet of therolling element. Further, in a case of using the rolling bearingaccording to the present invention for high speed rotation, it isdesirable to use a cermet of low density as the material for the rollingelement. Further in a case where a large load is applied or an impactload is given to the rolling bearing according to the present invention,it is desirable to use a superhard alloy of higher toughness as thematerial of the rolling element.

Rolling bearings for test (inner diameter: 12 mm, outer diameter: 28 mm,width: 8 mm, roll diameter: 4.76 mm, number of balls; 8) were measuredwith the materials shown in Table 14 and the following impact resistancetest and the rolling life test were conducted to each of the thusmanufactured test bearings.

TABLE 14 Corro- Impact resis- sion resis- Inner ring and outer ringRolling element tance tance Surface Surface Surface evalution evalutionNo. Material hardness Material hardening hardness value value Example 1Ti-6A1-4V 425-430 SUJ2 Chromizing 1050-1100 1.6 2.7 2 Ti-6A1-4V 425-43013% CrSUS Nv 1230-1350 1.7 3.0 nitridation 3 Ti-15Mo-5Zr-3A1 475-480SUJ2 Chromizing 1050-1100 1.6 3.1 4 Ti-15Mo-5Zr-3A1 475-480 13% CrSUS Nv1230-1350 1.8 3.6 nitridation 5 Ti-15Mo-5Zr 550-555 SUJ2 Chromizing1050-1100 1.7 2.9 6 Ti-15Mo-5Zr 550-555 13% CrSUS Nv 1230-1350 1.7 3.5nitridation Comp. 1′ SUS440C 670-675 Si₃Ni₄ — 1450-1570 1.0 1.0 Example2′ SUS440C 670-675 SUJ2 Chromizing 1050-1100 1.0 1.0 3′ SUS440C 670-67513% CrSUS Nv 1230-1350 1.2 1.1 nitridation 4′ Ti-6A1-4V 425-430 Si₃Ni₄ —1450-1570 1.2 2.3 5′ Ti-15Mo-5Zr-3A1 475-480 Si₃Ni₄ — 1450-1570 1.3 2.66′ Ti-15Mo-5Zr 550-555 Si₃Ni₄ — 1450-1570 1.2 2.5 7′ Ti-6A1-4V 425-430SUJ2 No 730-740 1.4 0.4 8′ Ti-15Mo-5Zr-3A1 475-480 13% CrSUS No 720-7301.6 1.3 9′ Ti-15Mo-5Zr 550-555 13% CrSUS No 720-730 1.5 1.2

The inner rings and the outer rings shown in Table 14 were obtained byany of the following methods (i) to (iv).

(i) At first, after machining a material comprising Ti-6Al-4V as the α+βtype titanium alloy, it was applied with a solution treatment of keepingat 950 to 1000° C. for one hour and then water cooled. Then, an agingtreatment of keeping at 450° C. for 20 hours and, subsequently, leavingin a furnace till 200° C. or lower was conducted. Then, grinding forfinishing was conducted. Thus, an inner ring and an outer ringcomprising a titanium alloy of a crystal tissue in which fine α phasewas dispersed in a matrix comprising the β phase and having a surfacehardness of Hv 425 to 430 were obtained.

(ii) At first, after machining a material comprising Ti-15Mo—SZr-3Al asthe β type titanium alloy, it was applied with a solution treatment ofkeeping at 800 to 850° C. for one hour and then water cooled. Then, anaging treatment of keeping at 425° C. for 17 hours, and further keepingat 475° C. for 7 hours, subsequently, leaving in a furnace till 200° C.or lower was conducted. Then, grinding for finishing was conducted.Thus, an inner ring and an outer ring comprising a titanium alloy of acrystal tissue in which the α phase finer than that in (i) above wasdispersed in a matrix comprising the β phase and having a surfacehardness of Hv 475 to 480 was obtained.

(iii) After machining a material comprising Ti-15Mo-5Zr, it was appliedwith a solution treatment of keeping at 800 to 8500C for one hour andthen water cooled. Then, an aging treatment of keeping at 450° C. for 20hours and, subsequently, leaving in a furnace till 200° C. or lower wasconducted. Then, grinding for finishing was conducted. Thus, an innerring and an outer ring comprising a titanium alloy of a crystal tissuein which the α phase finer than that in (i) above was dispersed in amatrix comprising β phase and having a surface hardness of Hv 550-550was obtained.

(iv) At first, a material comprising SUS 440C was machined into apredetermined shape. Then, after oil hardening under the conditions at akeeping temperature of 1000 to 1050° C. and at an oil temperature of 60°C., tempering was conducted under the conditions at 150 to 200° C. for 2hours. Then, grinding for finishing was conducted. Thus, an inner ringand the outer rings comprising SUS 440C and having a surface hardness ofHv 670 to 675 was obtained.

Further, the rolling element was obtained in any of the followingmethods (v) to (ix) which was manufactured such that the deviation fromspherical form was JIS grade G3 or higher, the surface roughness Ra was0.003 μm or less and the inter diametrical difference was 0.05 μm orless.

(v) At first, after machining a material comprising SUJ2 (high carbonchromium bearing steel class 2) into a predetermined shape, the chromiumdiffusion penetration treatment (indicated as [chromizing] in Table 14)was conducted under the conditions at 980 to 1050° C. for 10 hours.Then, after conducting oil hardening under the condition at a keepingtemperature of 830 to 850° C. and an oil temperature of 60° C.,tempering was conducted under the conditions at 150 to 200° C. for 2hours. Then, grinding for finishing was conducted. Thus, a ball formedat the surface with a chromium diffusion layer with a depth of 10 to 15μm (size corresponding to 2 to 3% of ball diameter) and having a surfacehardness of Hv 1050 to 1500 was obtained.

(vi) At first, a material comprising 13% Cr stainless steel (SUS) wasmachined into a predetermined shape. Then, after conducting oilhardening under the conditions at a keeping temperature of 1000 to 1050°C. and at an oil temperature of 60° C., tempering was conducted underthe conditions at 150 to 200° C. 2 hours. Then, the Nv nitridationtreatment described above (indicated as [Nv nitridation] in Table 14)was conducted under the conditions at 410 to 460° C. for 24 to 48 hours.Then, grinding for finishing was conducted. Thus, a ball formed at thesurface with a chromium diffusion layer with a depth of 10 to 15 μm(size corresponding to 2 to 3% of ball diameter) and having a surfacehardness of Hv 1230 to 1310 was obtained.

(vii) After machining a material comprising silicone nitride (Si₃N₄)into a predetermined shape, a grinding for finishing was conducted. Thusa ball having a hardness of Hv 1450 to 1570 was obtained.

(viii) At first, a material comprising SUJ 2 was machined into apredetermined shape. Then after conducting oil hardening under theconditions at a keeping temperature of 830 to 850° C. and at on oiltemperature of 60° C., tempering was conducted under the conditions at150 to 200° C. for 2 hours. Then, grinding for finishing was conducted.Thus, a ball comprising SUJ 2 and having a surface hardness HV 730 to740 was obtained.

(ix) A material comprising 13% Cr stainless steel was machined into apredetermined shape. Then after conducting oil hardening under theconditions at a keeping temperature of 1000 to 1050° C. and at an oiltemperature of 60° C., tempering was conducted under the conditions at150 to 200° C. for 2 hours. Then, grinding for finishing was conducted.Thus, a ball comprising 13% Cr stainless steel and having a surfacehardness Hv 720 to 730 was obtained.

Impact Resistance Test

An impact resistance test was conducted by the following method. Atfirst, each of the test bearings was attached to the rotational shaft ofan impact acceleration testing machine. Then, the test bearings weredropped from various heights in the axial direction (30-100 cm) in astate of attaching the rolling bearings and applying a preload at 9.6 Nand the impact acceleration upon dropping was measured by anacceleration gage. The test bearing was rotated before and after thedropping to measure the axial vibration acceleration (G value).

After the measurement, the minimum dropping height at which thedifference between the G value after dropping and the G value beforedropping was 5 mG or more was examined and the impact resistance wasjudged according to the impact acceleration at the dropping height. Theimpact resistance evaluation value in Table 14 is a comparative value ina case of evaluation based on the test result for No. 1′ (impactacceleration at the minimum dropping height where the difference of theG value before and after dropping was 5 mG or more) being assumed as 1.

Rolling Life Test

While rotating the test bearing under the following conditions, anaqueous solution of NaCl at 5 wt % solution was sprayed under thecondition of 1 ml on every 1 min to the rolling bearing. The rotationwas conducted while always measuring the axial vibratory acceleration (Gvalue) and the corrosion resistant rolling life was defined as a time toreaching the G value five times as much as the initial value. Theevaluation value for the corrosion resistance in Table 14 is acomparative value in a case of evaluation based on the test result forNo. 1′ (time to reach the G value five times as much as the initialvalue) being assumed as 1.

<Rotation condition> Radial load 78 N Axial load 20 N Rotational speed1000 rpm

The results are shown together in Table 14.

As can be seen from each of the test results in Table 14, Nos. 1 to 6corresponding to the examples of the present invention showed largervalues for both of the impact resistance and the corrosion resistancecompared with Nos. 1′ to 9′ as the comparative examples.

For the titanium alloy, β type (also including near β type) or (α+β)type is preferably used. The hardness of the titanium alloys can beincreased to Hv 400 to more by precipitation hardening of precipitatingfine α phase in β phase by applying a solution treatment from atemperature just below or just above the α/β transformation point toform β phase and then applying an aging treatment at 350 to 600° C.

For the rolling element, the following constitution (a) or (b) ispreferred;

(a) having a chromium diffusion layer as a corrosion resistant surfacehardening layer by the application of a chromium diffusion penetrationtreatment as a surface hardening treatment after formed with a highcarbon chromium bearing steel.

(b) having a dense and uniform nitride layer chromium diffusion layer asa corrosion resistant surface hardening layer by the application of anitridation treatment as a surface hardening treatment after formed withiron and steel material containing 3.0% by weight or more (preferably,8.0% by weight or more) of chromium.

The chromium diffusion penetration treatment (a) above is conducted, forexample, as described below. At first, a material to be treatedcomprising high carbon chromium bearing steel and a chemical formulatedfrom powdery chromium (Cr), powdery alumina (Al₂O₃) and powdery ammoniumchloride (NH₄Cl) are tightly sealed in a steel case and the case isplaced in a furnace. Then, the inside of the furnace is heated to900-1100° C. and kept for a predetermined time while flowing a hydrogen(H₂) gas or argon (Ar) in the casing.

Thus, chemical is reacted in the case to form vapors of chromiumchloride (CrCl₂). The chromium chloride conducts substitution reactionwith atoms forming the surface of the material to be treated by whichchromium diffuses and penetrates to the surface of the material to betreated. Alternatively, chromium formed by precipitation of chromiumchloride by reduction with hydrogen diffuses and penetrates to thesurface of the material to be treated. As a result, a chromium diffusionlayer is formed on the surface of the material to be treated. Thechromium diffusion layer has corrosion resistance and the surfacehardness is Hv 1050 to 1100.

Since the hardness of the core is lowered when applying gradual coolingafter the chromium diffusion and penetration treatment, it is preferredto harden the core by conducting hardening and tempering after thetreatment.

The nitridation treatment (b) is conducted, for example, as describedbelow. At first, fluoridation treatment was conducted to the material tobe treated comprising iron and steel material having 3.0% by weight(preferably, 8.0% by weight or more) of chromium by using, for example,a nitrogen fluoride (NF₃) gas at 200 to 400° C. Then, a nitridationtreatment is conducted by using an ammonia (NH₃) gas at 400 to 500° C.This method is referred to as an Nv nitridation treatment (registeredtrade mark of Air Water Co.).

In this method, an extremely dense and uniform nitride layer can beformed even when the nitridation treatment is conducted at a lowtemperature of 400 to 500° C. by applying a fluoridation treatment asthe pretreatment. The nitride layer has corrosion resistance and asurface hardness of Hv 1230 to 1350. Further, fine deformations can beprevented from being formed on the surface of the material to be treatedby applying the nitridation treatment at low temperature. Therefore,degradation of the dimensional accuracy of the rolling element by thesurface hardening treatment is prevented.

The reason for using the iron and steel material having 3.0% by weightor more (preferably, from 8.0% by weight or more) of chromium is thatthe hardness for the surface hardening layer is increased to a necessaryhardness for obtaining satisfactory wear resistance. That is, while thehardness of the surface hardening layer (b) can be improved by formingfine chromium nitride with chromium and nitrogen, a hardness requiredfor obtaining a satisfactory wear resistance can not be obtained whenthe chromium content is less than 3.0% by weight.

Further, in order not to cause coarse eutectic carbides by the Nvnitridation treatment, it is preferred to use an iron and steel materialcapable of satisfying: [C (%)]≦−0.05 [Cr(%)]+1.41.

The thickness (depth) of the surface hardening layer (a) and (b) ispreferably a size corresponding to 1.5 to 6% of the diameter for therolling element and is 100 μm or less.

The Young's modulus of the surface hardening layer formed by thetreatment (a) and (b) is substantially equal with the Young's modulus ofthe stainless steel or the bearing steel as the material to be treated(200-210 GPa), which is lower than the Young's modulus of 250 to 400 GPaof ceramics.

In the rolling bearing according to the present invention, the area ofcontact between the rolling element and the bearing ring is increased todecrease the contact face pressure compared with the rolling bearingdescribed in Japanese Published Unexamined Patent Application Hei11-223221. Accordingly, the sharing stress formed between the rollingelement and the bearing ring during rotation is moderated to cause lessrolling fatigue. Further, fine indentations are less caused to therolling element and the bearing ring when an impact load is applied fromthe outside.

FIG. 19 shows a rolling bearing according to another embodiment of thepresent invention. As shown in the drawing, the rolling bearing of thisembodiment comprises bearing rings 1 and 2 made of titanium alloy,rolling elements 3 interposed between the bearing rings 1 and 2, and aseal 5 sealed between the bearing rings 1 and 2 for preventing leakageof grease or intrusion of obstacles.

As the material for the bearing rings 1 and 2, a titanium alloy with aratio of the hardness to the Young' modulus (H/E) of 3.7 or more is usedand any of titanium alloys can be used suitably irrespective of theirkinds so long as the titanium alloy can satisfy: 3.7≦(H/E). However, itis preferred to use α+β type or β type (also including near β type)titanium alloys capable of attaining high hardness by precipitationhardening by solution treatment and aging treatment. They include, forexample, α+β type titanium alloy: Ti-6Al-4V or β type titanium alloy:Ti-24V-4Al, Ti-15V-3Cr-3Sn-3Al and Ti-15Mo-5Zr-3Al.

In this case, when the β phase is formed with the solution treatment andthe α phase is precipitated to the soft β phase by the aging treatment,the hardness at least from the surface to 2.5% Da (Da; diameter forrolling element) can be set to Hv 420 or more thereby increasing (H/E)to 3.7 or more.

Further, for the rolling element 3 as the rolling element, a rollingelement made of iron and steel material or ceramic material can be used.

However, when the corrosion resistance is required, it is preferred touse a rolling element made of stainless steel or ceramic as the rollingelement 3. When reduction weight is required particularly, it ispreferred to use a rolling element made of ceramics such as siliconnitride series, silicon carbide series, aluminum oxide series orzirconium oxide series. Further, in a case where a violent impact isloaded, it is preferred to use a rolling element made of iron and steelmaterial constituted with high carbon chromium steel such as SUJ2,martensitic stainless steel such as SUS 440C, 13 Cr system or high speedsteel represented by M50 which are excellent in toughness and havinglower Young's modulus compared with ceramics.

Further, the grease to be sealed has no particular restriction and anyof greases having a usable temperature range may be used.

The seal 5 has no particular restriction on the material and anymaterial can be used so long as it is within a usable temperature rangebut a seal made of rubber such as nitrile rubber that is easily deformedelastically along with elastic deformation of the bearing rings 1 and 2is used preferably.

Then, the operation and the like of the rolling bearing of theconstitution described above are to be explained.

Since the bearing rings 1 and 2 are bearing rings made of titaniumalloys, they have low Young's modulus and are easily deformedelastically. Accordingly, when impact is transmitted, for example, fromaxles to the bearing, since the bearing rings locally deform elasticallyto play a role of a spring that absorbs impact, impact transmitted tothe machine main body is decreased. Accordingly, in such an applicationuse as care-aid instruments such as a wheel chair, sports instrumentssuch as a roller blade or bicycles in which impacts or vibrations aredirectly transmitted from axles to the instrument main body or user,since the impact or vibration is moderated by the use of the rollingbearings according to the present invention, it can be used suitably.

Further, since the material is made of titanium alloy and the ratio ofthe hardness to the Young' modulus (H/E) is set to 3.7 or more, theindentation resistance and the rolling life are improved. Accordingly,it can be used suitably even in a case where impact or vibration isloaded to the bearing or in a case where there is a worry that obstaclesintrude into the bearings.

Furthermore, when the grease is used as the lubricant, since the greasefunctions as a damper for the vibration or impact, moderation of impactand vibration and indentation resistance are further improved.

While ball bearings are shown as the example of the rolling bearing inthe embodiments described above, it may be a roller bearing.

The rolling bearing according to the present invention was manufacturedby the method shown below. Grease was sealed as a lubricant.

For the bearing ring, one of α+β type titanium alloy (Ti-6Al-4V) or βtype titanium alloy (Ti-15V-3Cr-3Sn-3Al, Ti-22v-4Al, Ti-15Mo-5Zr-3Al)was used to manufacture a bearing ring for the rolling bearing ofbearing No. 6001. After machining, solution treatment and agingtreatment were applied and then grinding was applied.

The solution treatment was conducted by the following method. That is,for the α+β titanium alloy: Ti-6Al-4V, the solution treatment wasconducted by keeping at a temperature of 950 to 1000° C. for one hourand then water-cooling. Further, for the β type titanium alloys:Ti-15V-3Cr-3Sn-3Al, Ti-22V-4Al and Ti-15Mo-5Zr-3Al, the solutiontreatment was conducted by keeping at a temperature of 750 to 850° C.for one hour and water-cooling.

For the aging treatment, after keeping at a temperature of 400° C. to600° C. for 6 to 30 hours, cooling in the furnace was conducted down to200° C. to conduct the aging treatment.

For the rolling element, a rolling element made of ceramics such as,silicon nitride series, silicon carbide series, zirconium oxide seriesand aluminum oxide series and a rolling element made of 13% Cr systemmartensitic stainless steel were used.

A mineral oil type grease is used for the grease. Further, nitrilerubber seal was used for the seal 5 and a case made of polyamide wasused for the cage.

Further, as comparative examples, bearing rings were manufactured withmartensitic stainless steel (SUS440C) and precipitation hardening typestainless steel (SUS 630). The martensitic stainless steel (SUS 440c)was applied with oil hardening from a temperature of 900 to 950° C. andapplied with tempering at 150 to 200° C. The precipitation hardeningtype stainless steel (SUS 630) was applied with a solution treatment ata temperature from 920-970° C. and applied with an aging treatment at450-500° C.

For each of the rolling bearings manufactured under the conditionsdescribed above, an indentation resistance test and a rolling type testwere conducted.

Indentation Resistance Test

For the indentation resistance test, an outer ring 1 made of titaniumalloy cut into ¼ size was used. A spherical rolling element 3 made ofsilicon nitride having a diameter of 4.76 mm was pressed against theraceway surface of the bearing ring (outer ring 1) cut into ¼ and a loadat 980N was loaded to the raceway surface of the bearing ring 1 by wayof the rolling element 3 in this state. Then, the maximum depth of theindentation formed to the raceway surface at a portion applied with theload was measured.

Table 15 shows the test results for the indentation resistance test(indentation depth) and FIG. 20 shows a relation between the test resultof the indentation resistance test and H/E.

TABLE 15 2-5% Da Young's Indenta- Material for bearing Material forhardness modulus tion depth Rolling No. ring rolling element H (Hv) E(GPa) H/E (μm) life ratio Example 1 Ti-6A1-4V Alumina 421 113 3.7 1.12.4 ceramics 2 Ti-6A1-4V 13Cr stainless 434 113 3.8 1.0 2.5 steel 3Ti-15V-3Cr-3Sn-3A1 Silicon carbide 436 109 4.0 0.8 2.4 ceramics 4Ti-22V-4A1 Silicon nitride 440 105 4.2 0.9 2.6 ceramics 5 Ti-22V-4A113Cr stainless 463 105 4.4 0.8 2.7 steel 6 Ti-15Mo-5Zr-3A1 Alumina 473109 4.3 0.9 2.6 ceramics 7 Ti-15Mo-5Zr-3A1 13Cr stainless 483 109 4.40.7 2.8 steel 8 Ti-15Mo-5Zr-3A1 Silicon carbide 495 109 4.5 0.8 2.8ceramics 9 Ti-15Mo-5Zr-3A1 Silicon nitride 519 109 4.8 0.8 2.6 ceramics10 Ti-15Mo-5Zr-3A1 Zirconia 548 110 5.0 0.7 2.7 ceramics Comp. 1′Ti-6A1-4V Silicon nitride 385 113 3.4 2.0 2.0 Example ceramics 2′Ti-22V-4A1 13Cr stainless 405 111 3.6 1.6 1.9 steel 3′ SUS440 13Crstainless 667 210 3.2 2.4 1.7 steel 4′ SUS630 Silicon nitride 485 2002.4 4.8 1.0 ceramics

As can be seen from Table 15 and FIG. 20, Nos. 1 to 10 corresponding tothe examples of the present invention show smaller values for the depthof indentations formed on the raceway surface compared with Nos. 1′ to4′ as the comparative examples. This is because the ratio of thehardness to the Young's modulus (H/E) of the material for the bearingring is 2.4 to 3.6 in the bearings Nos. 1 to 4′, whereas the ratio ofthe hardness to the Young's modulus (H/E) for the material of thebearing ring is 3.7 or more in Nos. 1 to 10.

Rolling Life Test

A rolling life test was conducted by the following method. At first, aninitial vibration value of the bearing is measured when the inner ringis rotated under the conditions at a number of rotation of 500 rpm, aradial load of 69N and an axial load of 20N. Then, the rolling bearingis detached from a rolling life testing machine and the bearing isdropped from 1 m height in a state of applying a preload of 20 N withthe end face of the rolling bearing being directed to the surface of thefloor. Subsequently, the bearing is again set to the rolling lifetesting machine and the vibration value of the bearing when the innerring is rotated under the same conditions as described above ismeasured. Then, the instance that the measured value exceeds five timesthe initial vibration value was evaluated as the rolling life.

FIG. 15 shows the test result of the rolling life test (rolling liferatio) and FIG. 21 shows a relation between the test results of therolling life test and H/E. the roiling life ratios in Table 15 and FIG.21 are comparative values when evaluation is made based on the rollinglife of No. 4′ being assumed as 1.

As can be seen from Table 15 and FIG. 21, Nos. 1 to 10 corresponding tothe examples of the present invention show larger values for the rollinglife ratio compared with Nos. 1′ to 4′ as the comparative examples. Thisis because the ratio of the hardness to the Young's modulus (H/E) forthe material of the bearing ring is 2.4 to 3.6 in the bearings Nos. 1′to 4′, whereas the ratio of the hardness to the Young's modulus (H/E)for the material of the bearing ring is 3.7 or more in the bearings Nos.1 to 10.

Accordingly, it is possible to improve the impact resistance and thewear resistance of the bearing ring made of the titanium alloy byincreasing H/E of the bearing ring made of the titanium alloy as:3.7≦(H/E).

Further, as apparent from the result of the indent resistance test andthe rolling life test as described above, there is no substantialdifference in the effect between a case where H/E is 3.7 to 4.8 andexceeds 4.8 and since heat treatment or shot peening is required forincreasing the H/E value and the cost is increased by so much, H/E ispreferably within a range from 3.7 to 4.8 for the bearing ring made ofthe titanium alloy.

Rolling bearings for test were manufactured with the materials shown inTable 16 and the following rolling life test was conducted as below foreach of the test bearings. That is, the vibration values were measuredwhen the inner ring for each of the test bearings was rotated under theconditions at a radial load of 49N and a rotational speed of 1000 m⁻¹and the rolling life of the bearing was evaluated as an instance thatthe measured value reached twice the initial vibration value just afterstarting the rotation. In this case, the circumstantial temperature waschanged in accordance with the pattern shown in FIG. 22.

In a case where the material for the bearing ring is made of Ti-6Al-4V,a titanium alloy after applied with a solution treatment at atemperature of 920 to 1000° c. and then applied with an aging treatmentat a temperature of 450 to 550° C. was used as shown in Table 16.Further, in a case where the material for the bearing ring was made ofTi-15Mo-5Zr-3Al, a titanium alloy applied with a solution treatment at atemperature of 770 to 850° C. and then applied with an aging treatmentat a temperature of 400 to 500° C. for 10 to 60 hours was used. Further,in a case where the material of the bearing ring was made of Ti-22V-4A1,a titanium alloy applied with a solution treatment at a temperature of700 to 800° C. and then applied with an aging treatment at a temperatureof 400 to 500° C. for 5 to 40 hours was used. Cooling in the solutiontreatment was conducted by water-cooling and cooling in the agingtreatment was conducted by furnace cooling.

TABLE 16 Rolling Inner ring/outer life No. ring Rolling element α₂/α₁ratio Example 1 Ti-6A1-4V Silicone carbide 0.4 2.0 ceramics 2 Ti-6A1-4VZirconia ceramics 1.2 2.6 3 Ti-15Mo-5Zr-3A1 WC—Co superhard alloy 0.72.5 4 Ti-15Mo-5Zr-3A1 Silicon carbide 0.5 2.1 ceramics 5 Ti-15Mo-5Zr-3A1Alumina ceramics 0.9 2.8 6 Ti-15Mo-5Zr-3A1 Zirconia ceramics 1.3 2.3 7Ti-22V-4A1 TiC—Ni cerment 0.9 2.5 8 Ti-22V-4A1 Alumina ceramics 0.9 2.7Comp. 1′ Ti-GA1-4V Silicon nitride 0.3 1.0 Example ceramics 2′Ti-15Mo-5Zr-3A1 SUJ2 1.4 1.2 3′ Ti-22V-4A1 SUJ2 1.5 0.9 4′ Berylliumcopper Silicon carbide 0.2 0.3 ceramics 5′ Beryllium copper WC—Cosuperhard alloy 0.3 0.5 6′ SUS630 Silicon nitride 0.3 1.2 ceramics

Table 16 shows the test result of the rolling life test (rolling liferatio) and FIG. 23 shows a relation between the test results of therolling life test and the linear expansion coefficient ratio α₂/α₁ (α₁:linear expansion coefficient of the material for the bearing ring, α₂:linear expansion coefficient of the material for the rolling element).The rolling life ratio in Table 16 and FIG. 23 are comparative valueswhen evaluated based on the rolling life for No. 1′ being assumed as 1.

As can be seen from Table 16 and FIG. 23, Nos. 1 to 8 corresponding tothe examples of the present invention show larger values for the rollinglife ratio compared with Nos. 2′ and 3′ as the comparative examples.This is because the linear expansion coefficient ratio between thematerial for the bearing ring and the material for the rolling elementis: α₂/α₁≧1.4 in Nos. 2′ and 3′, whereas the linear expansioncoefficient ratio between the material for the bearing ring and thematerial for the rolling element is: α₂/α₁≦1.3 in Nos. 1 to 8. Further,Nos. 1 to 8 corresponding to the examples of the present invention showlarger values for the rolling life ratio compared with Nos. 1′, 4′ to 6′as the comparative examples. This is because the linear expansioncoefficient ratio between the material for the bearing ring and thematerial for the rolling element is: α₂/α₁≦0.3 in Nos. 1′ and 4′ to 6′,whereas the linear expansion coefficient ratio between the material forthe bearing ring and the material for the rolling element is: α₂/α₁≧0.4in. Nos. 1 to 8.

Accordingly, it can be seen that rolling life of excellent durabilitycan be obtained even in a circumstance where circumstantial temperaturevaries greatly by setting the linear expansion coefficient ratio betweenthe material for the bearing ring and the material for the rollingelement as 0.4≦α₂/α₁≦1.3. Further, since change for the gap in thebearing and preload and fitting stress can be moderated by setting thelinear expansion coefficient ratio between the material for the bearingring and the material for the rolling element to 0.4≦α₂/α₁≦1.3, therotational performance of the bearing is stabilized even when thecircumstantial temperature fluctuates.

FIG. 24 shows a further embodiment of the rolling bearing according tothe present invention. In the drawing, the rolling bearing comprises aninner ring 2 externally fitted and secured to the outer circumferentialsurface of a shaft to be supported (not illustrated), an outer ring 1disposed to the outer circumference of the inner ring 2 and pluralspherical rolling elements 3 disposed rotationally between the outerring 1 and the inner ring 2 and a cage 4 for holding the sphericalrolling elements 3 in an equi-distance relative to the circumferentialdirection of the rolling rings 11 and 12. Shield plates 9 are disposedon both axial ends of the bearing rings 11 and 12 for closing the openspace formed on both sides of the rolling element 3.

In this embodiment, the inner ring 1 and the outer ring 1 each comprisesa titanium alloy having a hardness of Hv 420 or more (for example, α+βtype titanium alloy, near β type titanium alloy and β type titaniumalloy) with the specific permeability being 1.001 or less. The rollingelement 3 comprises ceramics such as electroconductive zirconia orsilicon nitride, preferably, electroconductive ceramics with thespecific permeability being 1.001 or less.

The cage 4 is formed, for providing the cage itself with an electricinsulation and self lubricancy, for example, by adding a solid lubricantsuch as PTFE, MAC, graphite, N-lauro L-lysin, hBN and fluoro mica to aresin material, for example, fluoro-containing resin, PEEK, PEEK-PBI,PPS, TPI, PEN, PFA, ETFE, FEP, PCTFE, ECTFE and PVDF.

The shield plate 9 comprises titanium at a purity of 99.5% or higher andthe specific permeability of the shield plate 9 is 1.001 or less.Further, the shield plate 9 is formed as a ring, and fitting portions 9a that fit detachably to shield plate holding grooves 1 a and 1 a formedto the inner circumferential surface of the outer ring 1 are formed tothe outer circumferential surface of the plate.

As described above, when the inner ring 2 and the outer ring 1 areformed of the titanium alloy and the rolling element 3 is formed ofceramics, the specific permeability of the inner ring 2, the outer ring1 and the rolling element 3 is 1.001 or less. Thus, since the magneticflux density at the periphery of the bearing does not change greatly bythe rotation of the inner ring 2 or the outer ring 1, it can be used toequipments using electron beams such as wafer inspection apparatus.Further, when the shield plate 9 is formed of titanium at a purity of99.5% or higher, the specific permeability of the shield plate 9 is1.001 or less. Thus, since electron beams irradiated to the rollingelement 4 or the cage 4 can be shielded by the shield plate 9, charge upof the rolling element 3 by the electron beams can be prevented toprevent occurrence of halation. Further, when the resin of the cage 4 isformed with a resin, since the specific permeability of the cage 4 is1.001 or less, and the cage 4 is not charged up by electron beams whenit is irradiated by the electron beams, occurrence of halation can beprevented. Further, since a solid lubricant is added in the resinconstituting the cage 4 to provide the cage 4 with self-lubricancy, thecage itself functions as a lubricant and it can be used preferably evenin a vacuum atmosphere where the use of lubricant or grease isdifficult.

Rolling bearings for test shown in Table 17 were manufactured and thefollowing magnetic flux density change measuring test and the bearingwear test were conducted to each of the manufactured test bearings. Asthe titanium alloy (material for inner and outer rings) shown in Table17, those applied with the solution treatment and the aging treatmentunder the conditions shown in Table 18 were used.

TABLE 17 Outer Material for inner Material Change of Halation upondiametrical ring/outer ring Rolling for shield Material for magneticelectron surface wear No. material element plate cage field irradiationratio Example 1 Ti-15Mo-5Zr-3A1 Conductive Pure Ti Fluoro resin No No0.22 zirconia (JIS 2nd type) 2 Ti-15Mo-5Zr-3A1 Silicon ↑ ↑ No No 0.18nitride 3 Ti-15Mo-5Zr-3A1 Silicon ↑ ↑ No No 0.12 (oxidation) nitride 4Ti-15Mo-5Zr-3A1 Silicon ↑ ↑ No No 0.18 nitride (Ti film) 5Ti-15Mo-5Zr-3A1 Alumina ↑ ↑ No No 0.19 ceramics (TiN film) 6Ti-15V-3Cr-3Sn-3A1 Conductive ↑ ↑ No No 0.22 zirconia 7 Ti-22V-4A1Silicon ↑ ↑ No No 0.25 nitride 8 Ti-6A1-4V Silicon ↑ ↑ No No 0.19nitride 9 Ti-22V-4A1 Silicon ↑ ↑ No No 0.24 nitride (TiN film) 10Ti-6A1-4V Silicon ↑ ↑ No No 0.29 nitride TiN film Comp. 1′Ti-15Mo-5Zr-3A1 Silicon — Fluoro resin No Present 0.23 Example nitride2′ Ti-15Mo-5Zr-3A1 Silicon SUS 304 Fluoro resin present No 0.21 nitride3′ Ti-22V-4A1 Silicon SPCC Fluoro resin Present No 0.20 nitride 4′Ti-15V-3Cr-3Sn-3A1 Silicon Pure Ti SUS 304 Present No 0.23 nitride (JIS2nd type) 5′ Ti-15V-3Cr-3Sn-3A1 Silicon Pure Ti SPCC Present No 0.22nitride (JIS 2nd type) 6′ Be—Cu Be—Cu Be—Cu Be—Cu No No 1.00

TABLE 18 Kind Solution condition Aging condition Ti-15V-3Cr-3Sn-750-800° C. × 1 Hr Atmospheric air: 450° C. × 3A1 (water cooling) 20 Hr(gradual cooling) Ti-22V-4A1 750-800° C. × 1 Hr Atmospheric air: 450° C.× (water cooling) 20 Hr (gradual cooling) Ti-6A1-4V 950-1000° C. × 1 HrAtmospheric air: 400° C.- (water cooling) 500° C. × 20 Hr (air cooling)Ti-15Mo-5Zr-3A1 735-850° C. × 1 Hr Atmospheric air: 425° C. ×(Oxidation) (water cooling) 20 Hr (gradual cooling) + Atmospheric air:475° C. × 7 Hr (gradual cooling) Ti-15Mo-5Zr-3A1 735-850° C. × 1 HrVacuum: 425° C. × (water cooling) 20 Hr (gradual cooling + Vacuum: 475°C. × 7 Hr (gradual cooling)

Magnetic Flux Density Change Measuring Test

A magnetic flux density change measuring test was conducted by thefollowing method. That is, as shown in FIG. 5, after attaching a testbearing 10 to a rotational shaft 13 disposed in magnetic fields of apermanent magnet 16, the rotational shaft 13 was rotated at a speed ofabout 200 rpm during which the change of magnetic flux density wasmeasured by a tesla meter 17. Then, for the maximum output of the teslameter shown in FIG. 6, those showing 0.1 mT or more are evaluated aswith change of the magnetic flux density and those with less than 0.1 mTwere evaluated as with no change of the magnetic flux density.

Bearing Wear Test

A bearing wear test was conducted by the following method. That is, asshown in FIG. 25, a silicon wafer 33 was supported by three testbearings 10 and the silicon wafer 33 was loaded and unloaded whileirradiating electron beams from an electron gun 32 to the silicon wafer33. Then, after repeating loading/unloading of the silicon wafer 33 for150,000 cycles, the amount of wear for the outer ring of the testbearing 10 was measured. Simultaneously, absence or presence for theoccurrence of halation at the portion of the rolling bearing in a caseof irradiating electron beams was confirmed by a detector 31.

Table 17 shows the test results for the magnetic flux density changemeasuring test and the bearing wear test. The wear ratio as the resultof the bearing wear test in Table 17 is a comparative value in a case ofevaluation based on the amount of wear in the outer ring of No. 6′ beingassumed as 1.

As can be seen from the test result in Table 17, Nos. 1 to 10 as theexamples of the present invention show smaller values for the wearamount on the surface of the outer ring compared with No. 6′. This isbecause the bearing ring of No. 6′ is formed of beryllium copper,whereas the bearing ring of Nos. 1 to 10 are formed of titanium alloysharder than beryllium copper.

Further, Nos. 1 to 10 as the examples of the present invention showsmaller values for the change of the magnetic flux density compared withNos 4′ and 5′ as the comparative examples. This is because the cage forNos. 4′ and 5′ are formed of iron and steel materials such as SUS 304and SPCC, whereas the cage for Nos. 1 to 10 are formed of resins such asfluoro resin.

Further, Nos. 1 to 10 as the examples of the present invention showsmaller values of the probability for the occurrence of halation due toelectron beams compared with Nos. 2′ and 3′. This is because the shieldplate of the bearings for 2′ and 3′ are formed of iron and steelmaterials such as SUS 304 and SPCC, whereas the shield plate for thebearings of Nos. 1 to 10 are formed of titanium at a purity of 99.5% orhigher.

Accordingly, it can be seen that a rolling bearing which can be usedsuitably in a circumstance where corrosion resistance and non-magneticproperty are required by forming the rolling element with ceramics,forming the cage with the resin and forming the shield plate withtitanium at a purity of 99.5% or higher.

Nos. 4, 5, 8 as the examples of the present inventions are examples offorming a hard film such as of TiN on the surface of a rolling elementmade of ceramics and electroconductivity can be ensured by forming thehard film such as of TiN on the surface of the rolling element made ofceramics.

As the kind of the titanium alloys used as the constituent material forthe bearing ring, titanium alloys hardened by aging treatment (forexample, α+β type titanium alloy, near β type titanium alloy and β typetitanium alloy) are preferred and they can include, specifically,Ti-6Al-4V, Ti-62 46, Ti-15Mo-5Zr-3Al, Ti-22V-4Al, Ti-15Mo-3Cr-3Sn-3Al.In addition, any of titanium alloys having a hardness of Hv 420 or moreby age-hardening treatment can be used suitably.

When more excellent seizure resistance and wear resistance are required,the sliding property on the surface of the bearing ring can further beimproved by heating the titanium alloy in atmospheric air to applyoxidation thereby forming an oxide layer comprising TiOx (0<x<2) on thesurface of the titanium alloy. In this case, when the temperature forthe oxidation treatment is set to 400 to 500° C., which is thetemperature for the aging treatment, the age-hardening treatment and theoxidation treatment can be conducted simultaneously, as well as theoxide layer formed within this temperature range becomes highly denseand the close adhesion can be improved preferably. Further when thetitanium alloy is applied with the solution treatment at a temperatureof 700 to 1000° C. and further applied with oxidation treatment afterpolishing, an oxide film can be formed on the rolling surface of thebearing ring of the titanium alloy. In this case, a further preferredsliding property can be obtained by applying super finishing to therolling surface of the bearing ring made of the titanium alloy and thenapplying the oxidation treatment.

In equipments utilizing electron beams such as a wafer inspectionapparatus, it is required to form an surrounding atmosphere to a highvacuum atmosphere of 10⁻⁴ Pa or higher. Therefore, in the rollingbearing used in equipments that utilize electron beams, a lubricatingoil or grease can not be used as the lubricant. When the cage is formedof a resin having a self-lubricity, the lubricating property can beenhanced to improve the ware resistance of the rolling bearing. Further,when the cage is formed of a resin, the specific permeability of thecage is 1.001 or less, so that the magnetic flux density does not changegreatly depending on the material of the cage and it is suitable for usein semiconductor manufacturing apparatus utilizing electron beams.

As the material for the cage, fluoro-containing resin, polyether etherketone (PEEK), copolymer of polyether ether ketone andpolybenzoimidazole (PEEK-PBI), polyphenylene sulfide (PPS),thermoplastic polyimide (TPI), polyether nitrile (PEN), thermoplasticaromatic polyamideimide, tetrafluoroethylene-perfluoro alkylvinyl ethercopolymer (PFA), tetrafluoroethylene-ethylene polymer (ETFE),tetrafluroethylene-hexafluoropropylene copolymer (FEP),polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylenecopolymer (PCTFE) and polyvinylidene fluoride (PVDF) are suitable.

As the solid lubricant to be added to the resin described above, atleast one of tetrafluoroethylene resin powder (PTFE), graphite,hexagonal boron nitride (hBN), fluoro mica, melamine cyanurate (MCA),amino acid compound having layered crystal tissue (N-lauro-L-lysine),fluoro graphite, fluoro pitch, molybdenum disulfide (MoS₂), tungstendisulfide (WS₂) can be used. Among them, PTFE, MAC, graphite,N-lauro-L-lysine, hBN and fluoro mica used alone or in a combination oftwo or more of them are more preferred in view of lubricity.

Since the ceramics forming the rolling element and the resin forming thecage are insulative material, when insulators are present at the wafersupporting portion of a semiconductor manufacturing apparatus,particularly, within a range which is visible as images near theelectron beams, the rolling element or the cage which is an insulator ischarged up to cause halation.

Further, in the bearing for supporting the wafer, if the bearing itselfhas no electroconductivity, since current does not flow to the inside ofthe bearing, no desired images can be obtained, for example, in a caseof length measuring SEM. Accordingly, the ceramics used as theconstituent material for the rolling element desirably haveelectroconductivity and, specifically, electroconductive zirconia seriesceramics are suitable.

Further, in a case of insulative ceramics such as silicon nitride seriesceramics and alumina series ceramics, ceramic coating films such as ofTiN, TiC, TiCN, TiAlN having conductivity is preferably applied to thesurface of the rolling element by a coating treatment such as PVC(Physical Vapor Deposition), CVD (Chemical Vapor Deposition) and thelike.

On the other hand, regarding the cage, it gives no effects on theconductivity of the bearing but since it is an insulator as describedabove, halation occurs upon irradiation of electron beams. Further,since the resin material for the cage is difficult to be applied withthe film deposition treatment, charge up can not be prevented by theconductive ceramic coating as in the case of the rolling element. Inview of the above, when the rolling bearing used in equipments utilizingelectron beams is constituted as a shield type rolling bearing having ametal shield plate, since the portion of the cage is concealed by theshield plate, occurrence of halation due to electron beams can beprevented.

Further, also in a case of using insulative ceramics to the rollingelement, occurrence of halation can be prevented with no effects on theperipheral magnetic fields by using a shield plate made of puretitanium.

Since the shield plate is manufactured by press molding, plasticfabrication at a room temperature is required. The material used for theshield plate has been austenitic stainless steel typically representedby SUS 304 and cold rolled steel plates (JIS SPCC, SPCD, SPCE) but anyof them is a material mainly comprising steel, the specific permeabilityis 1.001 or more which gives undesired effects on the peripheralmagnetic fields.

On the other hand, when the shield plate is formed of titanium at apurity of 99.5% or higher, the specific permeability of the shield plateis 1.001 or less. Thus, since the rotation of the shield plate does notcause such a change of the magnetic flux density as flexing the electronbeam in the peripheral magnetic fields, it is suitable as a shield platefor the rolling bearing used near the electron beam generation portion.Since pure titanium has excellent cold moldability, a thin plate can bemanufactured and since it can be fabricated by press molding, the shieldplate can be manufactured at a reduced cost.

As the titanium used for the shield plate material, any of JIS classes 1to 4 can be used suitably, with first and second classes of lessimpurity content being particularly preferred in view of the pressmoldability.

Suitable application use of the rolling device according to the presentinvention described above is as shown below.

Non Magnetic Property

Along with the trend of increasing the integration degree insemiconductor devices, dimensional reduction of integrated circuitpatterns formed to the wafer has been proceeded. While laser beams havebeen utilized, for example, in semiconductor production apparatus orwafer inspection apparatus but higher resolution power has been requiredalong with the dimensional reduction of the circuit pattern and thesystem has now been shifted to apparatus utilizing electron beams at ashorter wavelength and having higher resolution than the laser beams.

Electron beams are easily deflected even by slight magnetic fields tolower the writing accuracy and inspection accuracy of wafers. Therefore,along with the use of electron beams, a requirement for the non-magneticproperty of the rolling bearing used, for example, in the wafertransportation stage or a wafer supporting portion has been increased.In such semiconductor production apparatus utilizing the electron beams,when a rolling bearing made of non-magnetic stainless steel having aspecific permeability of about 1.01 to 1.1 is used, since it giveseffects on the electron beams and causes fluctuation of the magneticfields, a rolling bearing made of beryllium copper with a specificpermeability of 1.001 or less is used.

Since the titanium alloy is a completely non-magnetic material with thespecific permeability of 1.001 or less, it is suitable as a constituentmaterial for the rolling bearing or linear guide used in thesemiconductor production apparatus utilizing electron beams.

In a case of using the rolling bearing or the linear guide in thevicinity of an electron gun as an electron generation source, since therotational motion of the rolling bearing or the linear motion of thelinear guide causes fluctuation in the magnetic field to deflect theelectron beams, it is necessary that the specific permeability of therolling bearing or the linear guide is reduced to 1.001 or less.

The semiconductor production apparatus utilizing the electron beams caninclude specifically, for example, length measuring SEM, stepper,electron beam lithography system, and wafer defect inspection apparatusand the rolling device according to the present invention can be usedsuitably, for example, in a wafer supporting holder or a stage movingportion of the apparatus described above.

Further, the measuring apparatus utilizing the electron beams caninclude, specifically, a rotational portion of spectralized crystals ora specimen stage of an electron probe micro analyzer (EPMA), scanningelectron microscope (SEM), focusing ion beam FIB, transmission electronmicroscope (TEM), ESCA and Auger electron spectroscopic apparatus, andthe rolling device according to the present invention can be usedsuitably, for example, to an operating portion near the electrongeneration source.

Further, the semiconductor production apparatus using magnetic fieldscan include, for example, an etching apparatus of applying a voltageunder magnetic fields by an powerful permanent magnet, and the rollingdevice according to the present invention can be used suitably, forexample, to a joint portion of a conveyor robot arm for conveying wafersin the chamber.

The rolling bearing used in strong magnetic fields, for example, therolling bearing for supporting axle used near a super electroconductivemagnet of a linear motor car rotates while intersecting the strongmagnetic fields from a superelectroconductive magnet during rotation ofthe axle. Accordingly, when the rolling bearing is made of ferroelectricmaterial such as martensitic steel, it may be a worry that eddy currentis caused to generate heat in the rolling element or the bearing ring ofthe bearing and bring about seizure along with temperature elevation.

It is necessary that the bearing used in such strong magnetic fields beformed as non-magnetic material. The bearing ring of the rolling bearingaccording to the present invention is formed of the titanium alloy andhas a lower specific permeability than that of the non-magnetic steel.Accordingly, it causes less eddy current and can be used suitably.

The rolling bearing used in a nuclear magnetic resonance diagnosticapparatus lowers the inspection accuracy by the fluctuation of magneticfields along with rotation of the bearing. Since the bearing ring madeof the titanium alloy in the rolling bearing according to the presentinvention is completely non-magnetic with the specific permeabilitybeing 1.001 or less, it can be used suitably, for example, in therolling portion of the nuclear magnetic resonance diagnostic apparatus.

Corrosion Resistance

In a case of a rolling device such as a rolling bearing, a linear movingguide device or a ball screw used, for example, in a wafer cleaningapparatus, an alkaline solution such as an ammonia solution or astrongly acidic solution is used for the cleaning of the semiconductorwafer. Accordingly, intrusion of impurities into the semiconductormanufacturing steps due to the scattering of the alkaline solution orstrongly acidic solution or exposure in the vapors thereof results in asignificant problem. Further, since a corrosive gas is used in theetching apparatus, the corrosion resistance is required.

Since the rolling device according to the present invention has asufficient corrosion resistance even in an alkaline solution such as anammonia solution, it is possible to provide a bacteriocidal property bythe titanium oxide coating.

In the same manner, since corrosive chemicals are used in photographicdeveloping machines in the developing step or the fixing step, therolling bearing according as the present invention can be used suitablyalso to the bearings for supporting transportation conveyors in thephotographic developing machine or as the bearing used in the pump forsupplementing chemicals.

Reduced Weight—Compact Resistance/Young's Modulus

Since the bearing ring made of the titanium alloy of the rolling bearingaccording to the present invention has a specific gravity of about ⅔ forthat of the steel, the weight of the bearing ring can be reduced.

Since a hand piece in dental equipments for conducting drilling orcutting, since a dental cutting tool attached to a shaft is used whilebeing rotated at a super-high speed of 300,000 rpm or higher, a reducedweight and quietness are required. Accordingly, reduced weight and lownoise are required also for the bearing used in the hand piece of thedental equipments.

Since the bearing ring made of the titanium alloy has a specific gravityas low as about ⅔ for that of the steel, the weight of the hand piece isreduced. Further, since the rotational torque of the bearing is reducedand the noise can be reduced, the rolling bearing according to thepresent invention can be used suitably as a rolling bearing for use inthe dental hand piece.

Further, in driving motors, high power motors are used so that thenumber of a rotation reaches the maximum number of rotation in a shortperiod of time and driving motors having a great reserve in the powerfor actually required power upon conducting cutting or the like at themaximum number of rotation are used.

For decreasing the power of the driving motor, it may be considered toreduce the rising time from start up to the maximum number of rotation,to decrease the maximum number of rotation or to decrease the inertia ofthe rotational shaft that is rotationally driven by the driving motor.However, since the working efficiency is reduced when the rising time ismade longer or the maximum number of rotation is kept lower, it is mosteffective to decrease the inertia of the rotational shaft in order toreduce the power of the driving motor while maintaining the workingefficiency at a high accuracy.

For decreasing the inertia of the rotational shaft, it is necessary todecrease the weight of the rotational shaft and it is effective to usetitanium alloys (specific gravity: about 4.0-5.0) having a smallerspecific gravity compared with existent iron and steel materials(specific gravity: about 7.8) is preferred since the size of the devicecan be reduced and the consumption power of the driving motor can bedecreased without deteriorating the desired working efficiency.

Since the bearing rings made of titanium alloys have small Young'smodulus, the weight of bearing rings can be reduced in ball bearings,cylindrical roller bearings, tapered corn roll bearings, self alignedroller bearings for use in the driving system, for example, in generalindustrial machines or automobile transmissions and the weight of theentire apparatus can be reduced. Further, the rolling bearing accordingto the present invention is suitable since it is reduced in the weightand higher speed rotation is possible. Further, since the Young'smodulus of the bearing ring is small as ½ for that of the steel when anidentical load is applied, the rolling bearing made of the titaniumalloys has an effect of decreasing the surface pressure at a portion incontact with rolling elements to decrease the stress at the portion ofcontact, so that it has an effect capable of increasing the rollingfatigue strength.

In addition, when the rolling bearings according to the presentinvention are used as the angular ball bearings and the cylindricalroller bearings used under a high speed rotation of dmn=200,000 or moresuch as in spindles of machine tools and turbo chargers, since theinertia at high speed rotation is decreased, they can be used suitably.

In the bearing for use in a rotating anode X-ray tube, X-rays aregenerated by impinging thermoelectrons to a target attached to the topend of a rotating anode that supports the bearing, in which the shafthas to be grounded to the earth by way of the bearing in order toprevent charging on the target. Further, not ceramics but heat resistantiron and steel materials such as SKH are used irrespective of conditionsat vacuum, high speed and high temperature. Since the rolling bearingaccording to the present invention is reduced in the weight, it can berotated at a high speed, does not suffer from lowering in the hardnesseven at high temperature and further has electroconductivity, it can beused suitably as a bearing for use in the rotating anode X-ray tube. Inthis case, electroconductive ceramics are suitable as the rollingelement.

In part mounting machines used for electronic equipment production stepssuch as for computers and portable telephones, the speed of operationsof taking out precision parts such as semiconductor devices and mountingthem to substrate has been increased and, particularly, along withrecent demand for reducing the size of electronic equipments themselves,the size of semiconductor devices arranged on the substrates isdecreased and integration on the substrates has been progressed, so thatthe positioning accuracy in a case of mounting parts reaches an order ofas fine as several μm. Further, since the attaching speed has alsotended to be increased in order to improve the production efficiency ofsubstrates and parts are mounted at a high speed of 0.5 to 1.0 sec orless for 1 cycle, the operation speed of a linear moving device thatsupports the head is also increased. Further, a wire bonder thatconnects semiconductor devices mounted on the substrate to circuits hasa structure in which bearing portions of the linear guide rail are fixedand rails having a part mounting head secured at the top end is movedvertically. In many actual mounting machines, since a series ofattaching steps such as adsorption of parts, mounting and fixing of themon substrates are conducted continuously, a machine gun system has beenadopted in which plural rails are arranged on a drum and the parts aremounted continuously while rotating the drum. Vertical movement formounting the parts, as well as rotational acceleration by the rotationof the drum in synchronization with the vertical movement are given to alinearly moving rail, and the inertia caused by the own weight of therail and the own weight of the head exerts as a bending moment on therail. Particularly, when the cycle time for the vertical movement of therail is reduced to 0.1 sec or less, acceleration exerting on the railincreases to about several G—several tens G and, in addition,acceleration in the circumferential direction of the drum also increasesto about several G. Since the rolling device according to the presentinvention can be reduced greatly in the weight compared with existentdevices made of steel, it can decrease acceleration loaded on the railand can be used suitably as a linear moving guide device for use in partmounting machines.

Further, along with reduction in the size and the weight of automobiles,improvement in the performance and increase in the power have beendemanded in addition to the reduction in the size and the weight alsofor engine auxiliaries such as alternators, and larger vibrations andgreater loads (about 4G-20G as gravitational acceleration) along withhigh speed rotation under more stringent working conditions than usualare exerted simultaneously by way of belts, for example, on the bearingsfor use in alternators upon operation of the engine and they are usedunder high temperature condition (about 90-130° C.).

The rolling bearing according to the present invention is preferredsince it is reduced in the weight and can reduce the weight of theengine auxiliaries described above.

Further, in severe circumstances of large vibrations, great load andhigh temperature, tissue whitening changes are formed particularly nearthe maximum shearing stress position of a load area of an outer ring asa fixed ring in existent bearings made of steels and early peelingoccurs starting from the change of tissue as a trigger in about ⅕ to{fraction (1/20)} of the designed bearing life. Since the bearing madeof titanium alloy in the rolling bearing according to the presentinvention has a stable tissue and causes no change in the tissue asexemplified by the tissue whitening change, the life can be extended.

Low Heat Conductivity

Since rolling bearings for use in business equipments such as copyingmachines, laser beam printers (LBP) and facsimiles (for example,bearings for heat rolls and bearings for pressure rolls used in thefixing portion of LBP) are used under high temperature, for example, atabout 200 to 250° C., working conditions are further severe (about 100to 150° C. at the portions other than the fixing portion). In addition,recyclic use of the fixing portion is required for resource saving.Further, a characteristics of less releasing heat from the heat roll athigh temperature to the outside is also required for the heat roll athigh temperature for energy saving.

Since the heat conductivity of the titanium alloy is low among othermetal materials, when the rolling bearing using the bearing ring made oftitanium alloy as the bearing for use in the heat roll, the amount ofheat transmitted from the heat roll by way of the bearing to the outsidecan be reduced.

Linear Expansion Coefficient

In information recording apparatus such as video tape recorders (VTR) orhard disk devices (HDD), fineness of reproduced images and higherdensity for the information recording amount are desired and rotationalaccuracy has been improved. As a bearing for satisfying the requirementof high rotational accuracy, a so-called combined bearing unit in whichpreload is applied between two opposed rolling bearings has beenadopted. Loading of preload between the bearings can provide effectssuch as improvement of the rigidity for the main shaft, decrease ofrotation with deflection and avoidance of resonance frequency.

When the rolling element of the rolling bearing is formed of siliconnitride, the preload is sometimes decreased to lower the rotationalaccuracy of the main shaft. This is attributable to that the linearexpansion coefficient of the rolling element within the range of theworking temperature of the bearing (1-9.0×10⁻⁶/K) is much smallercompared with that of the bearing ring comprising bearing steel orstainless steel. That is, the amount of heat expansion of the rollingelement is smaller relative to the amount of heat expansion of thebearing ring by the temperature elevation upon rotation of the bearingand, correspondingly, the amount of the gap inside of the bearingsincreases, to reduce the preload initially applied between the bearingsand, depending on the case, this may cause complete loss of preload. Theloss of preload causes lowering of the rotational performance such asreduction of the rigidity of the shaft, increase in the rotation of theshaft with reflection and change of the resonance frequency of theshaft.

Further, another problem in a case of forming the rolling element withsilicon nitride is that the impact resistance of the bearing isdecreased. That is, when an excess impact load is applied from theoutside to the bearing, stress is localized to the rolling element andto the portion of contact between the bearing ring and the rollingelement and, as a result, minute indentation may sometimes be formed tothe raceway surface of the bearing ring. Occurrence of the indentationremarkably deteriorates the acoustic performance and vibrationalperformance of the bearing to result in lowering of the performance ofVTR or HDD. This is because the Young's modulus of the rolling elementis higher and the bearing ring less deforms elastically compared withthe case of forming the rolling element with bearing steel or stainlesssteel, which remarkably localizes the stress that causes indentations tothe raceway surface tending to cause indentations.

In this case, when the bearing ring is formed of the titanium alloy,since the linear expansion coefficient of the bearing ring is 8.0 to9.0×10⁻⁵/K, loss of preload is less caused. Further, it is suitable toform the rolling element with the zirconia series ceramics since thedifference of the linear heat expansion coefficient between the bearingring and the rolling element can be decreased.

Further, with regard to the impact resistance, since the Young's modulusof the rolling element is lower compared with a case of forming therolling element of the bearing steel or stainless steel and theoccurrence of indentations due to localized stress can be suppressedeven in a case of undergoing excess impact load, the acousticperformance or the vibrational performance of the bearing is notreduced.

What is claimed is:
 1. A rolling device comprising an outer member andan inner member each having a raceway surface and rolling elementshaving a rolling surface interposed between the raceway surfaces of theouter member and the inner member and rolling on the raceway surfaces byrotational or linear movement of the outer member or the inner member inwhich the outer member and/or the inner member comprises titanium alloythat has at least one of beta (β) phase, near beta (β) phase and mixedphases of alpha (α) and beta (β), at the room temperature respectively,wherein the outer member and/or the inner member has a raceway surfacehardness from Hv 400 or more to Hv 592 or less, the outer member and/orthe inner member has a core hardness of Hv420 or more and has an oxygencompound layer at the raceway surface, and the oxygen compound layercomprises titanium oxide containing rutile type TiO₂ and has a thicknessfrom 20 nm or more to 95 nm or less.
 2. A rolling device as defined inclaim 1, wherein the core hardness of the outer member and/or the innermember is Hv 450 or more and the thickness of the oxygen compound layercomprises titanium oxide containing rutile type TiO₂ is from 50 nm ormore to 95 nm or less.
 3. A rolling device as defined in claim 1,wherein the rolling elements comprise at least one of titanium alloys,silicon nitride, silicon carbide, zirconia series ceramics, aluminaseries ceramics and SIALON series ceramics.
 4. A rolling device asdefined in claim 1, wherein the outer member and/or the inner member hasa hard film on the raceway surface.
 5. A rolling device as defined inclaim 4, wherein the raceway surface formed with the hard film has asurface hardness of Hv of 350 or more.
 6. A rolling device as defined inclaim 4, wherein the raceway surface formed with the hard film has asurface hardness of Hv of 450 or more.
 7. A rolling device as defined inclaim 4, wherein the hard film comprises at least one of TiN, TiC, TiCN,TiAlN, CrN, SiC and diamond-like carbon.
 8. A rolling device as definedin claim 1, wherein all of the rolling elements comprise a superhardalloy or cermet.
 9. A rolling device comprising an outer member and aninner member each having a raceway surface, rolling elements havingrolling surfaces interposed between the raceway surfaces of the outermember and the inner member and rolling on the raceway surfaces byrotational or linear movement of the outer member or the inner memberand a cage for holding the rolling elements in which the outer memberand/or the inner member comprises titanium alloy that has at least oneof beta (β) phase, near beta (β) phase and mixed phases of alpha (α) andbeta (β) at the room temperature respectively, and the outer memberand/or the inner member has a raceway surface hardness from Hv 400 ormore to Hv 592 or less and the cage has a heat conductivity of 20W/(m·K) or more.
 10. A rolling device as defined in claim 9, wherein thecage comprises one of copper, tellurium copper, brass, aluminum bronze,phosphorus bronze, nickel silver, cupro nickel and beryllium copper. 11.A rolling device comprising an outer member and an inner member eachhaving a raceway surface and rolling elements having rolling surfacesinterposed between the raceway surfaces of the outer member and theinner member and rolling on the raceway surfaces by rotational or linearmovement of the outer member or the inner member in which at least oneof the outer member, the inner member and the rolling elements comprisestitanium alloy that has at least one of beta (β) phase, near beta (β)phase and mixed phases of alpha (α) and beta (β) at the room temperaturerespectively and one of the raceway surfaces of the outer member and theinner member and the rolling surfaces of the rolling elements has omega(ω) phase with the size of the crystal particles of 1 μm or less.
 12. Arolling device as defined in claim 11 wherein the size of the crystalparticles is 800 nm or less.
 13. A rolling device as defined in claim11, wherein the size of the crystal particles is 10 nm or less.
 14. Arolling device comprising an outer member and an inner member eachhaving a raceway surface and rolling elements having a rolling surfaceinterposed between the raceway surfaces of the outer member and theinner member and rolling on the raceway surfaces by rotational or linearmovement of the outer member or the inner member in which the outermember and/or the inner member comprises titanium alloy that has atleast one of beta (β) phase, near beta (β) phase and mixed phases ofalpha (α) and beta (β), at the room temperature respectively, whereinthe outer member and/or the inner member has a raceway surface hardnessfrom Hv400 or more to Hv592 or less, the outer member and/or the innermember has a hard film on the raceway surface and has a lubricating filmof 0.1 μm to 10 μm on the hard film.
 15. A rolling device as defined inclaim 14, wherein the outer member and/or inner member has a lubricatingfilm of 0.1 μm to 5 μm on the hard film.
 16. A rolling device as definedin comprising an outer member and an inner member each having a racewaysurface and rolling elements having a rolling surface interposed betweenthe raceway surfaces of the outer member and the inner member androlling on the raceway surfaces by rotational or linear movement of theouter member or the inner member in which the outer member and/or theinner member comprises titanium alloy that has at least one of beta (β)phase, near beta (β) phase and mixed phases of alpha (α) and beta (β),at the room temperature respectively, wherein the outer member and/orthe inner member has a raceway surface hardness from Hv400 or more toHv592 or less, the all of the rolling elements comprise a superhardalloy or cermet and have a heat conductivity of 35 W/(m·K) or more. 17.A rolling device as defined in claim 16, wherein all of the rollingelements have a heat conductivity of 50 W/(m·K) or more.
 18. A rollingdevice comprising an outer member and an inner member each having araceway surface and rolling elements having a rolling surface interposedbetween the raceway surfaces of the outer member and the inner memberand rolling on the raceway surfaces by rotational or linear movement ofthe outer member or the inner member in which the outer member and/orthe inner member comprises titanium alloy that has at least one of beta(β) phase, near beta (β) phase and mixed phases of alpha (α) and beta(β), at the room temperature respectively, wherein the outer memberand/or the inner member has a raceway surface hardness from Hv400 ormore to Hv592 or less, all of the rolling elements have a surfacehardening layer comprising an iron and steel material and has acorrosion resistance on the surface.
 19. A rolling device as defined inclaim 18, wherein the surface hardening layer is formed by applying achromium diffusion penetration treatment on the surface of a basematerial comprising all of the rolling elements.
 20. A rolling device asdefined in claim 18, wherein the surface hardening layer contains anitride layer formed by applying a nitridation treatment to the surfaceof a base material comprising all of the rolling elements.
 21. A rollingdevice comprising an outer member and an inner member each having araceway surface and rolling elements having a rolling surface interposedbetween the raceway surfaces of the outer member and the inner memberand rolling on the raceway surfaces by rotational or linear movement ofthe outer member or the inner member in which the outer member and/orthe inner member comprises titanium alloy that has at least one of beta(β) phase, near beta (β) phase and mixed phases of alpha (α) and beta(β), at the room temperature respectively, wherein the titanium alloysatisfies the condition: 3.7≦(H/E) where E (Gpa) represents the Young'smodulus and H (Hv) represents the minimum hardness from the racewaysurface to a depth of {fraction (2/100)} to {fraction (5/100)} of thediameter of the rolling element, the outer member and/or the innermember has a raceway surface hardness from Hv400 or more to Hv592 orless.
 22. A rolling device comprising an outer member and an innermember each having a raceway surface and rolling elements having arolling surface interposed between the raceway surfaces of the outermember and the inner member and rolling on the raceway surfaces byrotational or linear movement of the outer member or the inner member inwhich the outer member and/or the inner member comprises titanium alloythat has at least one of beta (β) phase, near beta (β) phase and mixedphases of alpha (α) and beta (β), at the room temperature respectively,wherein the titanium alloy satisfies the condition: 4.0≦(H/E) where E(Gpa) represents the Young's modulus and H (Hv) represents the minimumhardness from the raceway surface to a depth of {fraction (2/100)} to{fraction (5/100)} of the diameter of the rolling element, the outermember and/or the inner member has a raceway surface hardness from Hv400or more to Hv592 or less.
 23. A rolling device as defined in claim 21 or22 wherein (H/E) is 4.5 or less.
 24. A rolling device comprising anouter member and an inner member each having a raceway surface androlling elements having a rolling surface interposed between the racewaysurfaces of the outer member and the inner member and rolling on theraceway surfaces by rotational or linear movement of the outer member orthe inner member in which the outer member and/or the inner membercomprises titanium alloy that has at least one of beta (β) phase, nearbeta (β) phase and mixed phases of alpha (α) and beta (β), at the roomtemperature respectively, wherein the outer member and/or the innermember has a raceway surface hardness from Hv400 or more to Hv592 orless, the ratio α₂/α₁ between the heat expansion coefficient α₁ of theouter member and/or the inner member and the heat expansion coefficientα₂ of the rolling element is within a range of 0.4 to 1.3.
 25. A rollingdevice comprising an outer member and an inner member each having araceway surface and rolling elements having a rolling surface interposedbetween the raceway surfaces of the outer member and the inner memberand rolling on the raceway surfaces by rotational or linear movement ofthe outer member or the inner member in which the outer member and/orthe inner member comprises titanium alloy that has at least one of beta(β) phase, near beta (β) phase and mixed phases of alpha (α) and beta(β), at the room temperature respectively, wherein the rolling devicefurther comprises a shield plate for shielding an opening formed betweenthe outer member and the inner member and the shield plate is formed oftitanium at a purity of 99.5% or higher, the outer member and/or theinner member has a raceway surface hardness from Hv400 or more to Hv592or less.
 26. A rolling device as defined in claim 24, wherein each ofthe outer member and the inner member has an oxide film containingTiO_(x) (x=0-2) on its surface.
 27. A rolling device as defined in anyone of claims 11, 4, 15, 23 and 24 wherein all of the rolling elementscomprise at least one of titanium alloys, silicon nitride, siliconcarbide, zirconia series ceramics, alumina series ceramics and SIALONseries ceramics.
 28. A rolling device as defined in any one claims 4,15, 17, 20, 23 and 24 wherein the rolling device further comprises acage for holding the rolling elements and the cage comprises one ofcopper, tellurium copper, brass, aluminum bronze, phosphorus bronze,nickel silver, cupro nickel and beryllium copper.